Eradication Of Polio
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Polio eradication, the goal of permanent global cessation of circulation of the
poliovirus Poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species '' Enterovirus C'', in the family of '' Picornaviridae''. There are three poliovirus serotypes, numbered 1, 2, and 3. Poliovirus is composed ...
and hence elimination of the
polio Poliomyelitis ( ), commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 75% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe ...
myelitis (polio) it causes, is the aim of a multinational
public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the de ...
effort begun in 1988, led by the
World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
(WHO), the
United Nations Children's Fund UNICEF ( ), originally the United Nations International Children's Emergency Fund, officially United Nations Children's Fund since 1953, is an agency of the United Nations responsible for providing humanitarian and developmental aid to childre ...
(UNICEF) and the
Rotary Foundation The Rotary Foundation is a non-profit corporation that supports the efforts of Rotary International to achieve world understanding and peace through international humanitarian, educational, and cultural exchange programs. It is supported solely ...
. These organizations, along with the U.S.
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...
(CDC) and
The Gates Foundation The Gates Foundation is an American private foundation founded by Bill Gates and Melinda French Gates. Based in Seattle, Washington, it was launched in 2000 and is reported to be the third largest charitable foundation in the world, holding $7 ...
, have spearheaded the campaign through the
Global Polio Eradication Initiative The Global Polio Eradication Initiative is an initiative created in 1988, just after the World Health Assembly resolved to eradicate the disease poliomyelitis. Led by the World Health Organization, it is the largest international public health ...
(GPEI). Successful
eradication of infectious diseases The Extinction, eradication of infectious diseases is the reduction of the prevalence of an Infection, infectious disease in the Earth, global Host (biology), host population to zero. Two infectious diseases have successfully been eradicated ...
has been achieved twice before, with
smallpox Smallpox was an infectious disease caused by Variola virus (often called Smallpox virus), which belongs to the genus '' Orthopoxvirus''. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (W ...
in humans and
rinderpest Rinderpest (also cattle plague or steppe murrain) was an infectious viral disease of cattle, domestic water buffalo, and many other species of even-toed ungulates, including gaurs, African Buffalo, buffaloes, large antelope, deer, giraffes, wilde ...
in ruminants. Prevention of disease spread is accomplished by
vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...
. There are two kinds of
polio vaccine Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated vaccine, inactivated poliovirus given by injection (IPV) and a attenuated vaccine, weakened poliovirus given by mouth (OPV). The World Healt ...
—oral polio vaccine (OPV), which uses weakened poliovirus, and inactivated polio vaccine (IPV), which is injected. OPV is less expensive and easier to administer, and can spread immunity beyond the person vaccinated, creating
contact immunity Contact immunity is the property of some vaccines, where a vaccinated individual can confer immunity upon unimmunized individuals through contact with bodily fluids or excrement. In other words, if person "A" has been vaccinated for virus ''X'' ...
. It has been the predominant vaccine used. However, under conditions of long-term vaccine virus circulation in under-vaccinated populations,
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
s can reactivate the virus to produce a polio-inducing strain, while OPV can also, in rare circumstances, induce polio or persistent
asymptomatic Asymptomatic (or clinically silent) is an adjective categorising the medical conditions (i.e., injuries or diseases) that patients carry but without experiencing their symptoms, despite an explicit diagnosis (e.g., a positive medical test). P ...
infection in vaccinated individuals, particularly those who are
immunodeficient Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that affec ...
. IPV, being inactivated, does not carry these risks, but does not induce contact immunity. IPV is more costly and the logistics of its delivery are more challenging.
Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...
is the latest country to have officially stopped
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
transmission of wild poliovirus, with its last reported case in 2016. Of the three strains of WPV, the last recorded wild case caused by type2 (WPV2) was in 1999, and WPV2 was declared eradicated in 2015. Type3 (WPV3) is last known to have caused polio in 2012, and was declared eradicated in 2019. All wild-virus cases since that date have been due to type1 (WPV1). ,
Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...
and
Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
are the only two countries where the disease is still classified as endemic. Recent polio cases arise from two sources, the original "
wild Wild, wild, wilds or wild may refer to: Common meanings * Wilderness, a wild natural environment * Wildlife, an undomesticated organism * Wildness, the quality of being wild or untamed Art, media and entertainment Film and television * ''Wild ...
" poliovirus (WPV), and the much more prevalent mutated oral vaccine strains, known as circulating vaccine-derived poliovirus (cVDPV) or variant poliovirus. Vaccines against each of the three wild strains of polio have given rise to strains of cVDPV, with cVDPV2 being most prominent. cVDPV caused 312 confirmed paralytic polio cases worldwide in 2024, and was detected in 21 countries.


Factors influencing eradication of polio

Eradication of polio has been defined in various ways: # As elimination of the occurrence of poliomyelitis even in the absence of human intervention. # As
extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
of
poliovirus Poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species '' Enterovirus C'', in the family of '' Picornaviridae''. There are three poliovirus serotypes, numbered 1, 2, and 3. Poliovirus is composed ...
, such that the infectious agent no longer exists in nature or in the laboratory. # As control of an infection to the point at which
transmission Transmission or transmit may refer to: Science and technology * Power transmission ** Electric power transmission ** Transmission (mechanical device), technology that allows controlled application of power *** Automatic transmission *** Manual tra ...
of the disease ceased within a specified area. # As reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures. In theory, if the right tools were available, it would be possible to eradicate all infectious diseases that reside only in a human host. In reality, there are distinct biological features of the organisms and technical factors of dealing with them that make their potential eradicability more or less likely. Three indicators, however, are considered of primary importance in determining the likelihood of successful eradication: that effective interventional tools are available to interrupt transmission of the agent, such as a
vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...
; that diagnostic tools, with sufficient sensitivity and specificity, be available to detect infections that can lead to transmission of the disease; and that humans are required for the life-cycle of the agent, which has no other
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...
and cannot amplify in the environment.


Strategy

The most important step in eradication of polio is interruption of
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
transmission Transmission or transmit may refer to: Science and technology * Power transmission ** Electric power transmission ** Transmission (mechanical device), technology that allows controlled application of power *** Automatic transmission *** Manual tra ...
of poliovirus. Stopping polio transmission has been pursued through a combination of routine
immunization Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an infectious agent (known as the antigen, immunogen). When this system is exposed to molecules that are foreign to the body, called ' ...
, supplementary immunization campaigns, and surveillance of possible outbreaks. Several key strategies have been outlined for stopping polio transmission: # High infant immunization coverage with four doses of oral
polio vaccine Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated vaccine, inactivated poliovirus given by injection (IPV) and a attenuated vaccine, weakened poliovirus given by mouth (OPV). The World Healt ...
(OPV) in the first year of life in developing and endemic countries, and routine immunization with OPV or IPV elsewhere. # Organization of "national immunization days" to provide supplementary doses of oral polio vaccine to all children less than five years old. # Active surveillance for poliovirus through reporting and laboratory testing of all cases of acute flaccid paralysis. Acute flaccid paralysis (AFP) is a clinical manifestation of poliomyelitis characterized by weakness or
paralysis Paralysis (: paralyses; also known as plegia) is a loss of Motor skill, motor function in one or more Skeletal muscle, muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory d ...
and reduced
muscle tone In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state.O’Sullivan, S. B. (2007) ...
without other obvious cause (e.g., trauma) among children less than fifteen years old. Other pathogenic agents can also cause AFP, such as
enterovirus ''Enterovirus'' is a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteric' meaning intestinal). Serologic ...
es,
echovirus Echovirus is a polyphyletic group of viruses associated with enteric disease in humans. The name is derived from "enteric cytopathic human orphan virus". These viruses were originally not associated with disease, but many have since been identifi ...
es, and
adenovirus Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from t ...
es. # Expanded environmental surveillance to detect the presence of poliovirus in communities. Sewage samples are collected at regular and random sites and tested in laboratories for the presence of WPV or cVDPV. Since most polio infections are asymptomatic, transmission can occur in spite of the absence of polio-related AFP cases, and such monitoring helps to evaluate the degree to which virus continues to circulate in an area. # Targeted "mop-up" campaigns once poliovirus transmission is limited to specific geographical foci.


Vaccination

There are two distinct types of
polio vaccine Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated vaccine, inactivated poliovirus given by injection (IPV) and a attenuated vaccine, weakened poliovirus given by mouth (OPV). The World Healt ...
. Oral polio vaccine (OPV, or Sabin vaccine) contains attenuated poliovirus. OPV is delivered as oral drops or infused into sugar cubes. It is highly effective and inexpensive (about per dose in 2024) and its availability has bolstered efforts to eradicate polio. The vaccine confers long-term, possibly lifelong,
immunity Immunity may refer to: Medicine * Immunity (medical), resistance of an organism to infection or disease * ''Immunity'' (journal), a scientific journal published by Cell Press Biology * Immune system Engineering * Radiofrequence immunity ...
to the virus. Because of its route of administration, it induces an immunization of the intestinal mucosa that protects against subsequent infection, though multiple doses are necessary to achieve effective prophylaxis. Attenuated poliovirus derived from the oral polio vaccine is excreted, infecting and indirectly inducing
immunity Immunity may refer to: Medicine * Immunity (medical), resistance of an organism to infection or disease * ''Immunity'' (journal), a scientific journal published by Cell Press Biology * Immune system Engineering * Radiofrequence immunity ...
in unvaccinated individuals, and thus amplifying the effects of the doses delivered. The oral administration does not require special medical equipment or training. Taken together, these advantages have made it the favored vaccine of many countries, and it has long been preferred by the global eradication initiative. The primary disadvantage of OPV derives from its inherent nature. As an attenuated but active virus, it can induce vaccine-associated paralytic poliomyelitis (VAPP) in approximately one individual per every 2.7million doses administered. The live virus can circulate in under-vaccinated populations (circulating vaccine-derived poliovirus, cVDPV) and over time can revert to a neurovirulent form causing paralytic polio. Until recent times, a trivalent OPV containing all three virus strains was used, but with the eradication of wild poliovirus type2 this was phased out in 2016 and replaced with bivalent vaccine containing just types 1 and 3, supplemented with monovalent type2 OPV in regions with documented cVDPV2 circulation. A novel OPV2 vaccine (nOPV2) genetically modified to reduce the likelihood of disease-causing activating mutations was granted emergency licencing in 2021, and subsequently full licensure in December 2023. Genetically stabilsed vaccines targeting poliovirus types 1 and 3 are in development, with the intention that these will eventually completely replace the Sabin vaccines. The inactivated polio vaccine (IPV, or Salk) contains trivalent fully inactivated virus, administered by injection. This vaccine cannot induce VAPP nor do cVDPV strains arise from it, but it likewise cannot induce contact immunity and thus must be administered to every individual. Added to this are greater logistical challenges. Though a single dose is sufficient for protection, administration requires medically trained vaccinators armed with single-use needles and syringes. Taken together, these factors result in substantially higher delivery costs. Original protocols involved
intramuscular injection Intramuscular injection, often abbreviated IM, is the medical injection, injection of a substance into a muscle. In medicine, it is one of several methods for parenteral, parenteral administration of medications. Intramuscular injection may be ...
in the arm or leg, but recently
subcutaneous injection Subcutaneous administration is the insertion of medications beneath the skin either by injection or infusion. A subcutaneous injection is administered as a bolus (medicine), bolus into the subcutis, the layer of skin directly below the dermis and ...
using a lower dose (so-called fractional-dose IPV, fIPV) has been found to be effective, lowering costs and also allowing for more convenient and cost-effective delivery systems. The use of IPV results in serum immunity, but no intestinal immunity arises. As a consequence, vaccinated individuals are protected from contracting polio, but their intestinal mucosa may still be infected and serve as a reservoir for the excretion of live virus. For this reason, IPV is ineffective at halting ongoing outbreaks of WPV or cVDPV, but it has become the vaccine of choice for industrialized, polio-free countries. While IPV does not itself induce mucosal immunity, it has been shown to boost the mucosal immunity from OPV, and the WHO now favors a combined protocol. It is recommended that vulnerable children receive a dose of OPV at birth, then beginning at the age of six weeks a 'primary series' consisting of three OPV doses at least four weeks apart, along with one dose of IPV after 14 weeks. This combined IPV/OPV approach has also been used in outbreak suppression.


Herd immunity

Polio vaccination is also important in the development of
herd immunity Herd immunity (also called herd effect, community immunity, population immunity, or mass immunity) is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become i ...
. For polio to occur in a population, there must be an infecting organism (
poliovirus Poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species '' Enterovirus C'', in the family of '' Picornaviridae''. There are three poliovirus serotypes, numbered 1, 2, and 3. Poliovirus is composed ...
), a susceptible human population, and a cycle of
transmission Transmission or transmit may refer to: Science and technology * Power transmission ** Electric power transmission ** Transmission (mechanical device), technology that allows controlled application of power *** Automatic transmission *** Manual tra ...
. There is no animal reservoir for poliovirus, and the transmission cycle of polio is from one infected person to another person susceptible to the disease, usually through the fecal-oral route. If the vast majority of the population is immune to a particular agent, the ability of that
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
to infect another host is reduced; the cycle of transmission is interrupted, and the pathogen cannot reproduce and dies out. This concept, called community immunity or herd immunity, is important to disease eradication, because it means that it is not necessary to inoculate 100% of the population—a goal that is often logistically very difficult—to achieve the desired result. If the number of susceptible individuals can be reduced to a sufficiently small number through
vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...
, then the pathogen will eventually die off. Herd immunity is an important supplement to vaccination. According to the concept of herd immunity, the population for whom the vaccine fails is still protected by the immunity of those around them, and it can only be achieved when vaccination levels are high. It is estimated that the minimum herd immunity threshold for poliovirus eradication ranges from approximately 75% in wealthy high-hygiene populations to 97% in poorer environments. If routine immunization were to be stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.


Vaccine-derived poliovirus

While vaccination has played an instrumental role in the reduction of polio cases worldwide, the use of attenuated virus in the oral vaccine carries with it an inherent risk. The oral vaccine is a powerful tool in fighting polio in part because of its person-to-person transmission and resulting contact immunity. However, under conditions of long-term circulation in undervaccinated populations, the virus can accumulate mutations that reverse the attenuation and result in vaccine virus strains that themselves cause polio. As a result of such circulating vaccine-derived poliovirus (cVDPV) strains, polio outbreaks have periodically recurred in regions that have long been free of the wild virus, but where vaccination rates have fallen. Oral vaccines can also give rise to persistent infection in immunodeficient individuals, with the virus eventually mutating into a more virulent immunodeficiency-associated vaccine-derived poliovirus (iVDPV). In particular, the type2 strain seems prone to reversions, so in 2016 the eradication effort abandoned the trivalent oral vaccine containing attenuated strains of all three virus types and replaced it with a bivalent oral vaccine lacking the type2 virus, while a separate monovalent type2 vaccine (mOPV2) was to be used only to target existing cVDPV2 outbreaks. A novel oral vaccine targeting type2 (nOPV2) that has been genetically stabilized to make it less prone to give rise to circulating vaccine-derived strains received full licensure in December 2023, with similar vaccines targeting types 1 and 3 undergoing
clinical trials Clinical trials are prospective biomedical or behavioral research studies on human subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...
. Eradication efforts will eventually require all oral vaccination to be discontinued in favor of the use of injectable vaccines. These vaccines are more expensive and more difficult to deliver, and they lack the ability to induce contact immunity because they contain only killed virus, but they likewise are incapable of giving rise to vaccine-derived viral strains.


Surveillance

A global program of surveillance for the presence of polio and the poliovirus plays a critical role in assessment of eradication and in outbreak detection and response. Two distinct methods are used in tandem: acute flaccid paralysis (AFP) surveillance and environmental surveillance. Monitoring for AFP aims at identifying outbreaks of polio by screening patients displaying symptoms consistent with, but not exclusive to, severe poliovirus infection. Stool samples are collected from children presenting with AFP and evaluated for the presence of poliovirus by accredited laboratories in the Global Polio Laboratory Network. Since rates of non-polio AFP are expected to be constant and large compared to the number of polio cases, the frequency of non-polio AFP reported in a population is indicative of the effectiveness of surveillance, as is the proportion of AFP patients from whom high-quality stool samples are collected and tested, with a target of at least 80%. Environmental surveillance is used to supplement AFP surveillance. This entails the routine testing of sewage samples for the presence of virus, which not only allows the effectiveness of vaccination efforts to be evaluated in countries with active transmission, but also allows the detection of new outbreaks in countries without known transmission. In 2018, the GPEI conducted environmental surveillance in 44 countries, 24 of which are in Africa.


Obstacles

Among the greatest obstacles to global polio eradication are the lack of basic health infrastructure, which limits vaccine distribution and delivery, the crippling effects of civil war and internal strife, and the sometimes oppositional stance that marginalized communities take against what is perceived as a potentially hostile intervention by outsiders. Another challenge has been maintaining the
potency Potency may refer to: * Potency (pharmacology), a measure of the activity of a drug in a biological system * Virility * Cell potency, a measure of the differentiation potential of stem cells * In homeopathic dilutions, potency is a measure of ho ...
of live (attenuated) vaccines in extremely hot or remote areas. The oral polio vaccine must be kept at for vaccination to be successful. An independent evaluation of obstacles to polio eradication requested by the WHO and conducted in 2009 considered the major obstacles in detail by country. In Afghanistan and Pakistan, the researchers concluded that the most significant barrier was insecurity, but that managing human resources, political pressures, the movement of large populations between and within both countries, and inadequately resourced health facilities also posed problems, as did technical issues with the vaccine. In
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
, the major challenge appeared to be the high efficiency of transmission within the populations of
Bihar Bihar ( ) is a states and union territories of India, state in Eastern India. It is the list of states and union territories of India by population, second largest state by population, the List of states and union territories of India by are ...
and
Uttar Pradesh Uttar Pradesh ( ; UP) is a States and union territories of India, state in North India, northern India. With over 241 million inhabitants, it is the List of states and union territories of India by population, most populated state in In ...
states, set against the low (~80% after three doses against type1)
seroconversion In immunology, seroconversion is the development of specific antibodies in the blood serum as a result of infection or immunization, including vaccination. During infection or immunization, antigens enter the blood, and the immune system begins t ...
response seen from the vaccine. In Nigeria, the most critical barriers identified were management issues, in particular the highly variable importance ascribed to polio by different authorities at the local government level, although funding issues, community perceptions of vaccine safety, inadequate mobilisation of community groups, and issues with the
cold chain A cold chain is a supply chain that uses refrigeration to maintain perishable goods, such as pharmaceuticals, produce or other goods that are temperature-sensitive. Common goods, sometimes called cool cargo, distributed in cold chains include fr ...
also played a role. In those countries where international spread from endemic countries had resulted in the reestablishment of transmission, namely
Angola Angola, officially the Republic of Angola, is a country on the west-Central Africa, central coast of Southern Africa. It is the second-largest Portuguese-speaking world, Portuguese-speaking (Lusophone) country in both total area and List of c ...
,
Chad Chad, officially the Republic of Chad, is a landlocked country at the crossroads of North Africa, North and Central Africa. It is bordered by Libya to Chad–Libya border, the north, Sudan to Chad–Sudan border, the east, the Central Afric ...
, and
South Sudan South Sudan (), officially the Republic of South Sudan, is a landlocked country in East Africa. It is bordered on the north by Sudan; on the east by Ethiopia; on the south by the Democratic Republic of the Congo, Uganda and Kenya; and on the ...
, the key issues identified were underdeveloped health systems and low routine vaccine coverage, although the low level of resources committed to Angola and South Sudan for the purpose of curtailing the spread of polio and climatic factors was also identified as playing a role. Two additional challenges are found in unobserved polio transmission and in vaccine-derived poliovirus. First, most individuals infected with poliovirus are asymptomatic or exhibit minor symptoms, with fewer than 1% of infections leading to paralysis, and most infected people are unaware that they carry the disease, allowing polio to spread widely before cases are seen. In 2000, using new screening techniques for the molecular characterization of outbreak viral strains, it was discovered that some of the outbreaks were actually caused by circulating vaccine-derived poliovirus, following mutations or recombinations in the attenuated strain used for the oral polio vaccine. This discovery altered the strategy for the discontinuation of vaccination following polio eradication, necessitating an eventual switch to the more expensive and logistically more problematic inactivated polio vaccine, as continued use of the oral inactivated virus would continue to produce such revertant infection-causing strains. The risk of vaccine-derived polio will persist long after the switch to inactivated vaccine, as a small number of chronic excretors continue to produce active virus for years (or even decades) after their initial exposure to the oral vaccine. In a 2012 interview with Pakistani newspaper ''Dawn'', Dr. Hussain A. Gezari, the WHO's special envoy on global polio eradication and primary healthcare, gave his views on obstacles to eradication. He said that the biggest hurdle preventing Pakistan from becoming polio-free was holding district health officials properly accountable—in national eradication campaigns officials had hired their own relatives, even young children. Gezari asked, "How do you expect a seven-year-old thumb-sucking kid to implement a polio campaign of the government?" and added that, in spite of this, "the first national campaign was initiated by your government in 1994 and that year Pakistan reported 25,000 polio cases, and the number was just 198 last year, which clearly shows that the programme is working."


Opposition to vaccination efforts

One factor contributing to the continued circulation of polio immunization programs has been opposition to vaccination in some countries. In one country, Pakistan, "more than 200 polio team workers" have been killed (team members include not only vaccinators but police and security personnel) from "targeted killing and terrorism" while working on polio campaigns, (the killers motivated by the belief, spread by "radical clerics", that the vaccine is part of "a Western plot to sterilize Muslims"). In the context of the
United States invasion of Afghanistan Shortly after the September 11 attacks in 2001, the United States declared the war on terror and subsequently led a multinational military operation against Taliban-ruled Afghanistan. The stated goal was to dismantle al-Qaeda, which had exe ...
and the subsequent 2003 invasion of Iraq, rumours arose in the Muslim world that immunization campaigns were using intentionally-contaminated vaccines to sterilize local Muslim populations or to infect them with
HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...
. In Nigeria these rumours fit in with a longstanding suspicion of modern biomedicine, which since its introduction during the era of
colonialism Colonialism is the control of another territory, natural resources and people by a foreign group. Colonizers control the political and tribal power of the colonised territory. While frequently an Imperialism, imperialist project, colonialism c ...
has been viewed as a projection of the power of western nations. Refusal of vaccination came to be viewed as resistance to western expansionism, and when the contamination rumours led the Nigerian Supreme Council for Sharia to call for a region-wide boycott of polio vaccination, polio cases in the country increased more than five-fold between 2002 and 2006, with the uncontrolled virus then spreading across Africa and globally. In Afghanistan and Pakistan, fears that the vaccine contained contraceptives were one reason given by the
Taliban , leader1_title = Supreme Leader of Afghanistan, Supreme leaders , leader1_name = {{indented plainlist, * Mullah Omar{{Natural Causes{{nbsp(1994–2013) * Akhtar Mansour{{Assassinated (2015–2016) * Hibatullah Akhundzada (2016–present) ...
in issuing ''
fatwa A fatwa (; ; ; ) is a legal ruling on a point of Islamic law (sharia) given by a qualified Islamic jurist ('' faqih'') in response to a question posed by a private individual, judge or government. A jurist issuing fatwas is called a ''mufti'', ...
s'' against polio vaccination. Religious boycotts based on contamination concerns have not been limited to the Muslim world. In 2015, after claiming that a tetanus vaccine contained a contraceptive, a group of Kenyan Catholic bishops called on their followers to boycott a planned round of polio vaccination. This did not have a major effect on vaccination rates, and dialog along with vaccine testing forestalled further boycott calls. Other religion-inspired refusals arise from concern over whether the virus contains pig-derived products, and hence are ''
haram ''Haram'' (; ) is an Arabic term meaning 'taboo'. This may refer to either something sacred to which access is not allowed to the people who are not in a state of purity or who are not initiated into the sacred knowledge; or, in direct cont ...
'' (forbidden) in Islam, concern that vaccine production may have involved a prohibited taking of animal life, or a resistance to interfering with disease processes perceived to be divinely-directed. Concerns were addressed through extensive outreach, directed both toward the communities involved and respected clerical bodies, as well as promoting local ownership of the eradication campaign in each region. In early 2012, some parents refused to get their children vaccinated in
Khyber Pakhtunkhwa Khyber Pakhtunkhwa (; ; , ; abbr. KP or KPK), formerly known as the North West Frontier Province (NWFP), is a Administrative units of Pakistan, province of Pakistan. Located in the Northern Pakistan, northwestern region of the country, Khyber ...
(KPK) and in the
Federally Administered Tribal Areas The Federally Administered Tribal Areas, commonly known as FATA, was a semi-autonomous tribal region in north-western Pakistan that existed from 1947 until being merged with the neighbouring province of Khyber Pakhtunkhwa in 2018 through the ...
(FATA) but religious refusals in the rest of the country had "decreased manifold". Even with the express support of political leaders, polio workers or their accompanying security guards have been kidnapped, beaten, or assassinated. Skepticism in the Muslim world was exacerbated when it was learned that in 2011 the
Central Intelligence Agency The Central Intelligence Agency (CIA; ) is a civilian foreign intelligence service of the federal government of the United States tasked with advancing national security through collecting and analyzing intelligence from around the world and ...
(CIA) had conducted a fake
hepatitis B Hepatitis B is an infectious disease caused by the '' hepatitis B virus'' (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection. Many people have no symptoms during an initial infection. ...
immunization campaign, hoping to collect blood samples from
Osama bin Laden's compound in Abbottabad Osama bin Laden's compound, known locally as the Waziristan Haveli (), was a large, upper-class house within a walled compound used as a safe house for militant leader Osama bin Laden, who was Killing of Osama bin Laden, shot and killed there b ...
in order to confirm the genetic identity of the children living there, and by implication his own presence, leading directly to his killing. In a letter written to CIA director
Leon Panetta Leon Edward Panetta (born June 28, 1938) is an American retired politician and government official who has served under several Democratic administrations as secretary of defense (2011–2013), director of the CIA (2009–2011), White House chi ...
, the InterAction Alliance, a union of about 200 U.S.-based non-government organizations, deplored the actions of the CIA in using a vaccination campaign as a cover. Pakistan reported the world's highest number of polio cases (198), in 2011. and more than 60 polio vaccination workers were killed between December 2012 and April 2014. In May 2014, CIA director John Brennan prohibited his agency both from using vaccinations to cover operations and from testing samples collected by authentic vaccination campaigns. Polio vaccination efforts have also faced resistance in another form. The priority placed on vaccination by national authorities has turned it into a bargaining chip, with communities and interest groups resisting vaccination, not due to direct opposition, but to leverage other concessions from governmental authorities. In Nigeria this has taken the form of 'block rejection' of vaccination that is only resolved when state officials agree to repair or improve schools and health-care facilities, pave roads or install electricity. There have been several instances of threatened boycotts by health workers in Pakistan over payment disputes. Some governments have been accused of withholding vaccination or the necessary accompanying infrastructure from regions where opposition to their rule is high.


Polio eradication criteria

A country is regarded as polio-free or non-endemic if no cases have been detected for a year. However, it is still possible for polio to circulate under these circumstances, as was the case for Nigeria, where a particular strain of virus resurfaced after five years in 2016. This can be due to chance, limited surveillance and under-vaccinated populations. Moreover, for WPV1—the only type of the virus which is currently circulating following the eradication of WPV2 and WPV3—only 1 in 200 infection cases exhibit symptoms of polio paralysis in non-vaccinated children. Therefore, even a single case is indicative of an epidemic. Certification of wild poliovirus eradication requires three consecutive years without case reports, in the presence of reliable disease surveillance networks. Wild poliovirus type2 was certified eradicated in 2015, the last case having been detected in 1999. Wild poliovirus type3 has not been detected since 2012, and was certified eradicated in 2019.


Post-eradication plans

Beginning at certification of complete WPV eradication, the post-certification strategy will come into effect, with program priorities shifting towards outbreak preparedness and containment of existing virus material rather than circulating disease. Vaccination for WPV1 will cease one year following eradication certification, and eradication of vaccine-derived poliovirus is then targeted for 2030. Where possible, the number of facilities conducting operations with poliovirus is to be reduced significantly; and the use of wild poliovirus is to be abandoned altogether in favour of genetically stabilized attenuated strains where possible. there are 74 designated Poliovirus Essential Facilities (PEFs) across 24 countries where work on poliovirus can be carried out. These facilities are currently involved in producing materials to assist the eradication initiative, and perform crucial research which may prevent future outbreaks. After certification, these facilities retain the equipment and materials to continue vaccine production in the event of deliberate or accidental release. Work on Poliovirus outside of the PEFs will be prohibited, and stocks in laboratories that are not designated as PEFs must either be transferred to a PEF or destroyed.


Timeline


1950s–1987

Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries.
Czechoslovakia Czechoslovakia ( ; Czech language, Czech and , ''Česko-Slovensko'') was a landlocked country in Central Europe, created in 1918, when it declared its independence from Austria-Hungary. In 1938, after the Munich Agreement, the Sudetenland beca ...
became the first country in the world to scientifically demonstrate nationwide eradication of poliomyelitis in 1960. In 1962—just one year after Sabin's oral polio vaccine (OPV) was licensed in most industrialized countries—
Cuba Cuba, officially the Republic of Cuba, is an island country, comprising the island of Cuba (largest island), Isla de la Juventud, and List of islands of Cuba, 4,195 islands, islets and cays surrounding the main island. It is located where the ...
began using the oral vaccine in a series of nationwide polio campaigns. The early success of these mass vaccination campaigns suggested that polioviruses could be globally eradicated. The Pan American Health Organization (
PAHO The Pan American Health Organization (PAHO) is a specialized agency of the United Nations (UN) in charge of international health cooperation in the Americas. It fosters technical cooperation among member countries to fight communicable and non ...
), under the leadership of
Ciro de Quadros Ciro Carlos Araujo de Quadros (January 30, 1940 – May 28, 2014) was a Brazilian leader in the field of Public Health, in particular, the area of vaccines and preventable diseases. He was born in Rio Pardo, Brazil. Eradication of polio De Quadr ...
, launched an initiative to eradicate polio from the
Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...
in 1985. Much of the work towards eradication was documented by Brazilian photographer
Sebastião Salgado Sebastião Ribeiro Salgado Júnior (8 February 1944 – 23 May 2025) was a Brazilian social documentary photographer and photojournalist. He traveled in more than 120 countries for his photographic projects, which appeared in numerous press p ...
, as a
UNICEF Goodwill Ambassador UNICEF Goodwill Ambassador is an official postnominal honorific title, title of authority, legal status, and job description assigned to those goodwill ambassadors and activists, advocates who are designated by the United Nations. The UNICEF, ...
, in the book ''The End of Polio: Global Effort to End a Disease''.


1988–2000

In 1988, the
World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
(WHO), together with
Rotary International Rotary International is one of the largest service organizations in the world. The self-declared mission of Rotary, as stated on its website, is to "provide service to others, promote integrity, and advance world understanding, goodwill, and p ...
,
UNICEF UNICEF ( ), originally the United Nations International Children's Emergency Fund, officially United Nations Children's Fund since 1953, is an agency of the United Nations responsible for providing Humanitarianism, humanitarian and Development a ...
, and the U.S.
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...
(CDC) passed the
Global Polio Eradication Initiative The Global Polio Eradication Initiative is an initiative created in 1988, just after the World Health Assembly resolved to eradicate the disease poliomyelitis. Led by the World Health Organization, it is the largest international public health ...
(GPEI), with the goal of eradicating polio by the year 2000. The initiative was inspired by
Rotary International Rotary International is one of the largest service organizations in the world. The self-declared mission of Rotary, as stated on its website, is to "provide service to others, promote integrity, and advance world understanding, goodwill, and p ...
's 1985 pledge to raise $120million toward immunising all of the world's children against the disease. The last case of
wild Wild, wild, wilds or wild may refer to: Common meanings * Wilderness, a wild natural environment * Wildlife, an undomesticated organism * Wildness, the quality of being wild or untamed Art, media and entertainment Film and television * ''Wild ...
poliovirus poliomyelitis in the Americas was reported in
Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...
, August 1991. On 20 August 1994, the Americas were certified as polio-free. This achievement was a milestone in efforts to eradicate the disease. In 1994, the Indian Government launched the
Pulse Polio Pulse Polio is an immunisation campaign established by the government of India to eliminate poliomyelitis (polio) in India by vaccinating all children under the age of five years against the polio virus. The project fights polio through a la ...
Campaign to eliminate polio. The campaign involves annual vaccination of all children ages 0–5. In 1995, Operation MECACAR (
Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
,
Caucasus The Caucasus () or Caucasia (), is a region spanning Eastern Europe and Western Asia. It is situated between the Black Sea and the Caspian Sea, comprising parts of Southern Russia, Georgia, Armenia, and Azerbaijan. The Caucasus Mountains, i ...
, Central Asian Republics, and
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
) was launched; National Immunization Days were coordinated in 19
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
an and
Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
countries. In 1998, Melik Minas of
Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
became the last case of polio reported in Europe. In 1997, Mum Chanty of
Cambodia Cambodia, officially the Kingdom of Cambodia, is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. It is bordered by Thailand to the northwest, Laos to the north, and Vietnam to the east, and has a coastline ...
became the last person to contract polio in the
Indo-West Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the s ...
region. In 2000, the Western Pacific Region (including
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
) was certified polio-free. In October 1999, the last isolation of type2 poliovirus occurred in India. This type of poliovirus was subsequently declared eradicated. Also in October 1999, The CORE Group—with funding from the
United States Agency for International Development The United States Agency for International Development (USAID) is an agency of the United States government that has been responsible for administering civilian foreign aid and development assistance. Established in 1961 and reorganized in 1998 ...
(USAID)—launched its effort to support national eradication efforts at the grassroots level. The CORE Group commenced this initiative in
Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
, India, and
Nepal Nepal, officially the Federal Democratic Republic of Nepal, is a landlocked country in South Asia. It is mainly situated in the Himalayas, but also includes parts of the Indo-Gangetic Plain. It borders the Tibet Autonomous Region of China Ch ...
in South Asia, and in
Angola Angola, officially the Republic of Angola, is a country on the west-Central Africa, central coast of Southern Africa. It is the second-largest Portuguese-speaking world, Portuguese-speaking (Lusophone) country in both total area and List of c ...
,
Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...
, and
Uganda Uganda, officially the Republic of Uganda, is a landlocked country in East Africa. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the ...
in Africa.


2001–2005

By 2001, 575million children (almost one-tenth the world's population) had received some two billion doses of oral polio vaccine. The World Health Organization announced that Europe was polio-free on 21 June 2002, in the
Copenhagen Copenhagen ( ) is the capital and most populous city of Denmark, with a population of 1.4 million in the Urban area of Copenhagen, urban area. The city is situated on the islands of Zealand and Amager, separated from Malmö, Sweden, by the ...
Glyptotek Glyptotek or Glyptothek may refer to: * Ny Carlsberg Glyptotek, an art museum in Copenhagen, Denmark * Glyptothek, an art museum in Munich, Germany * ''Glyptothek (album)'', an album by Scottish musician Momus Momus (; Ancient Greek: Μῶμος ...
. In 2002, an outbreak of polio occurred in India. The number of planned polio vaccination campaigns had recently been reduced, and populations in northern India, particularly from the Islamic background, engaged in mass resistance to immunization. At this time, the Indian state
Uttar Pradesh Uttar Pradesh ( ; UP) is a States and union territories of India, state in North India, northern India. With over 241 million inhabitants, it is the List of states and union territories of India by population, most populated state in In ...
accounted for nearly two-thirds of total worldwide cases reported. (See the 2002 Global polio incidence map.) However, by 2004, India had adopted strategies to increase ownership of polio vaccinations in marginalized populations, and the immunity gap in vulnerable groups rapidly closed. In August 2003, rumors spread in some states in Nigeria, especially
Kano Kano may refer to: Places *Kano State, a state in Northern Nigeria *Kano (city), a city in Nigeria, and the capital of Kano State ** Kingdom of Kano, a Hausa kingdom between the 10th and 14th centuries ** Sultanate of Kano, a Hausa kingdom betwee ...
, that the vaccine caused sterility in girls. This resulted in the suspension of immunization efforts in the state, causing a dramatic rise in polio rates in the already endemic country. On 30 June 2004, the WHO announced that after a 10-month ban on polio vaccinations, Kano had pledged to restart the campaign in early July. During the ban the virus spread across Nigeria and into 12 neighboring countries that had previously been polio-free. By 2006, this ban would be blamed for 1,500 children being paralyzed, and had cost $450million for emergency activities. In addition to the rumors of sterility and the ban by Nigeria's Kano state, civil war and internal strife in
Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...
and
Côte d'Ivoire Ivory Coast, also known as Côte d'Ivoire and officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital city of Yamoussoukro is located in the centre of the country, while its largest city and ...
have complicated WHO's polio eradication goal. In 2004, 63% of all the polio cases in the world occurred in Nigeria (792 out of 1,265 total). In May 2004, the first case of the polio outbreak in Sudan was detected. The reemergence of polio led to stepped up vaccination campaigns. In the city of
Darfur Darfur ( ; ) is a region of western Sudan. ''Dār'' is an Arabic word meaning "home f – the region was named Dardaju () while ruled by the Daju, who migrated from Meroë , and it was renamed Dartunjur () when the Tunjur ruled the area. ...
, 78,654 children were immunized and 20,432 more in southern Sudan (Yirol and Chelkou). In 2005, there were 1,979 cases of wild poliovirus (excluding
vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...
-derived poliovirus). Most cases were located in two areas: the
Indian subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...
and
Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...
. Eradication efforts in the Indian sub-continent met with a large measure of success. Using the
Pulse Polio Pulse Polio is an immunisation campaign established by the government of India to eliminate poliomyelitis (polio) in India by vaccinating all children under the age of five years against the polio virus. The project fights polio through a la ...
campaign to increase polio immunization rates,
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
recorded just 66 cases in 2005, down from 135 cases reported in 2004, 225 in 2003, and 1,600 in 2002.
Yemen Yemen, officially the Republic of Yemen, is a country in West Asia. Located in South Arabia, southern Arabia, it borders Saudi Arabia to Saudi Arabia–Yemen border, the north, Oman to Oman–Yemen border, the northeast, the south-eastern part ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
, and
Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...
, countries that had been declared polio-free since before 2000, each reported hundreds of cases—probably imported from Nigeria. On 5 May 2005, news reports broke that a new case of polio was diagnosed in
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
, and the virus strain was suspected to be the same as the one that has caused outbreaks in Nigeria. New public fears over vaccine safety, which were unfounded, impeded vaccination efforts in Indonesia. In summer 2005, the WHO, UNICEF and the Indonesian government made new efforts to lay the fears to rest, recruiting celebrities and religious leaders in a publicity campaign to promote vaccination. In the United States on 29 September 2005, the Minnesota Department of Health identified the first occurrence of vaccine-derived poliovirus (VDPV) transmission in the United States since OPV was discontinued in 2000. The poliovirus type1 infection occurred in an unvaccinated,
immunocompromised Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that affe ...
infant girl aged seven months (the index patient) in an
Amish The Amish (, also or ; ; ), formally the Old Order Amish, are a group of traditionalist Anabaptism, Anabaptist Christianity, Christian Christian denomination, church fellowships with Swiss people, Swiss and Alsace, Alsatian origins. As they ...
community whose members predominantly were not vaccinated for polio.


2006–2010

In 2006, only four countries in the world (Nigeria, India,
Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
, and
Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...
) were reported to have endemic polio. Cases in other countries are attributed to importation. A total of 1,997 cases worldwide were reported in 2006; of these the majority (1,869 cases) occurred in countries with endemic polio. Nigeria accounted for the majority of cases (1,122 cases) but India reported more than ten times more cases in 2006 than in 2005 (676 cases, or 30% of worldwide cases). Pakistan and Afghanistan reported 40 and 31 cases respectively in 2006. Polio re-surfaced in
Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
after nearly six years of absence with 18 new cases reported. "Our country is not safe, as neighbours India and Pakistan are not polio free", declared Health Minister ASM Matiur Rahman. (See: Map of reported polio cases in 2006) In 2007, there were 1,315 cases of poliomyelitis reported worldwide. Over 60% of cases (874) occurred in India. In Nigeria, the number of polio cases fell dramatically, from 1,122 cases reported in 2006 to 285 cases in 2007. Officials credit the drop in new infections to improved political control in the southern states and resumed immunisation in the north, where Muslim clerics led a boycott of vaccination in late 2003. Local governments and clerics allowed vaccinations to resume on the condition that the vaccines be manufactured in Indonesia, a majority Muslim country, and not in the United States.
Turai Yar'Adua Turai Umar Musa Yar'Adua (born 26 July 1957) is the widow of the former Nigerian president and former Katsina State Governor, Umaru Musa Yar'Adua. She was the First Lady of Nigeria from 2007 until the death of her husband on 5 May 2010. Educa ...
, wife of recently elected Nigerian president
Umaru Yar'Adua Umaru Musa Yar'Adua (; 16 August 19515 May 2010) was a Nigerian politician who served as the president of Nigeria from 2007 until his death in May 2010. He won the Nigerian presidential election held on 21 April 2007, and was sworn in on 29 Ma ...
, made the eradication of polio one of her priorities. Attending the launch of immunization campaigns in
Birnin Kebbi Birnin Kebbi is a city located in Northwestern Nigeria It is the capital city of Kebbi State and headquarters of the Gwandu Emirate. As at 2007 the city had an estimated population of 125,594 people. Kebbi is mostly a Hausa and Fulani state, wit ...
in July 2007, Turai Yar'Adua urged parents to vaccinate their children and stressed the safety of oral polio vaccine. In July 2007, a student traveling from Pakistan imported the first polio case to
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
in over 20 years. Other countries with significant numbers of wild polio virus cases include the
Democratic Republic of the Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...
, which reported 41 cases, Chad with 22 cases, and Niger and
Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...
, each of which reported 11 cases. In 2008, 18 countries reported cases and the total number of cases was 1,651. Of these, 1,505 occurred in the four endemic countries and 146 elsewhere. The largest numbers were in Nigeria (798 cases) and India (559 cases): these two countries combined had 82.2 percent of all cases. Outside endemic countries, Chad reported the greatest number (37 cases). In 2009, a total of 1,604 cases were reported across 23 countries. Four endemic countries accounted for 1,256 of these, with the remaining 348 in 19 sub-Saharan countries with imported cases or re-established transmission. Once again, the largest numbers were in India (741) and Nigeria (388). All other countries had less than one hundred cases: Pakistan had 89 cases, Afghanistan 38,
Chad Chad, officially the Republic of Chad, is a landlocked country at the crossroads of North Africa, North and Central Africa. It is bordered by Libya to Chad–Libya border, the north, Sudan to Chad–Sudan border, the east, the Central Afric ...
64, Sudan 45,
Guinea Guinea, officially the Republic of Guinea, is a coastal country in West Africa. It borders the Atlantic Ocean to the west, Guinea-Bissau to the northwest, Senegal to the north, Mali to the northeast, Côte d'Ivoire to the southeast, and Sier ...
42, Angola 29,
Côte d'Ivoire Ivory Coast, also known as Côte d'Ivoire and officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital city of Yamoussoukro is located in the centre of the country, while its largest city and ...
26,
Benin Benin, officially the Republic of Benin, is a country in West Africa. It was formerly known as Dahomey. It is bordered by Togo to the west, Nigeria to the east, Burkina Faso to the north-west, and Niger to the north-east. The majority of its po ...
20,
Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...
19,
Burkina Faso Burkina Faso is a landlocked country in West Africa, bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to the south, and Ivory Coast to the southwest. It covers an area of 274,223 km2 (105,87 ...
15,
Niger Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...
15, the
Central African Republic The Central African Republic (CAR) is a landlocked country in Central Africa. It is bordered by Chad to Central African Republic–Chad border, the north, Sudan to Central African Republic–Sudan border, the northeast, South Sudan to Central ...
14,
Mauritania Mauritania, officially the Islamic Republic of Mauritania, is a sovereign country in Maghreb, Northwest Africa. It is bordered by the Atlantic Ocean to the west, Western Sahara to Mauritania–Western Sahara border, the north and northwest, ...
13, and
Liberia Liberia, officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to Guinea–Liberia border, its north, Ivory Coast to Ivory Coast–Lib ...
and
Sierra Leone Sierra Leone, officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered to the southeast by Liberia and by Guinea to the north. Sierra Leone's land area is . It has a tropical climate and envi ...
both had 11. The following countries had single-digit numbers of cases:
Uganda Uganda, officially the Republic of Uganda, is a landlocked country in East Africa. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the ...
with 8 cases,
Togo Togo, officially the Togolese Republic, is a country in West Africa. It is bordered by Ghana to Ghana–Togo border, the west, Benin to Benin–Togo border, the east and Burkina Faso to Burkina Faso–Togo border, the north. It is one of the le ...
6,
Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...
3, the
Democratic Republic of the Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...
3,
Burundi Burundi, officially the Republic of Burundi, is a landlocked country in East Africa. It is located in the Great Rift Valley at the junction between the African Great Lakes region and Southeast Africa, with a population of over 14 million peop ...
2, and
Mali Mali, officially the Republic of Mali, is a landlocked country in West Africa. It is the List of African countries by area, eighth-largest country in Africa, with an area of over . The country is bordered to the north by Algeria, to the east b ...
2. According to figures updated in April 2012, the WHO reported that there were 1,352 cases of wild polio across 20 countries in 2010. Reported cases of polio were down 95% in Nigeria (to a historic low of 21 cases) and 94% in India (to a historic low of 42 cases) compared to the previous year, with little change in Afghanistan (from 38 to 25 cases) and an increase in cases in Pakistan (from 89 to 144 cases). An acute outbreak in
Tajikistan Tajikistan, officially the Republic of Tajikistan, is a landlocked country in Central Asia. Dushanbe is the capital city, capital and most populous city. Tajikistan borders Afghanistan to the Afghanistan–Tajikistan border, south, Uzbekistan to ...
gave rise to 460 cases (34% of the global total), and was associated with a further 18 cases across Central Asia (
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...
and
Turkmenistan Turkmenistan is a landlocked country in Central Asia bordered by Kazakhstan to the northwest, Uzbekistan to the north, east and northeast, Afghanistan to the southeast, Iran to the south and southwest and the Caspian Sea to the west. Ash ...
) and the Russian Federation, with the most recent case from this region being reported from Russia 25 September. These were the first cases in the WHO European region since 2002. The Republic of the Congo (
Brazzaville Brazzaville () is the capital (political), capital and largest city of the Republic of the Congo. Administratively, it is a Departments of the Republic of the Congo, department and a Communes of the Republic of the Congo, commune. Constituting t ...
) saw an outbreak with 441 cases (30% of the global total). At least 179 deaths were associated with this outbreak, which is believed to have been an importation from the ongoing type1 outbreak in Angola (33 cases in 2010) and the Democratic Republic of the Congo (100 cases).


2011–2015

In 2011, 650 WPV cases were reported across sixteen countries: the four endemic countries—Pakistan, Afghanistan, Nigeria, and India—as well as twelve others. Polio transmission recurred in Angola, Chad and the Democratic Republic of the Congo.
Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...
reported its first case since 2009, while
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
reported 21 cases, mostly among the
Uyghurs The Uyghurs,. alternatively spelled Uighurs, Uygurs or Uigurs, are a Turkic peoples, Turkic ethnic group originating from and culturally affiliated with the general region of Central Asia and East Asia. The Uyghurs are recognized as the ti ...
of
Hotan Hotan (also known by other names) is a major oasis town in southwestern Xinjiang, an autonomous region in Northwestern China. The city proper of Hotan broke off from the larger Hotan County to become an administrative area in its own right i ...
prefecture,
Xinjiang Xinjiang,; , SASM/GNC romanization, SASM/GNC: Chinese postal romanization, previously romanized as Sinkiang, officially the Xinjiang Uygur Autonomous Region (XUAR), is an Autonomous regions of China, autonomous region of the China, People' ...
, the first non-imported cases since 1994. The total number of wild-virus cases reported in 2012 was 223, lower than any previous year. These were limited to five countries—Nigeria, Pakistan, Afghanistan, Chad, and Niger—of which all except Nigeria had fewer cases than in 2011. Several additional countries, Chad, the Democratic Republic of the Congo, Somalia, and Yemen, saw outbreaks of circulating vaccine-derived polio. The last reported type3 case of polio worldwide had its onset 11 November 2012 in Nigeria; the last wild case outside Nigeria was in April 2012 in Pakistan, and its absence from sewage monitoring in Pakistan suggests that active transmission of this strain has ceased there. A total of 416 wild-virus cases were reported in 2013, almost double the previous year. Of these, cases in endemic countries dropped from 197 to 160, while those in non-endemic countries jumped from 5 to 256. This was due to outbreaks in
Central Africa Central Africa (French language, French: ''Afrique centrale''; Spanish language, Spanish: ''África central''; Portuguese language, Portuguese: ''África Central'') is a subregion of the African continent comprising various countries accordin ...
(focused in
Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...
), the
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004), ...
, and the Middle East (focused in
Syria Syria, officially the Syrian Arab Republic, is a country in West Asia located in the Eastern Mediterranean and the Levant. It borders the Mediterranean Sea to the west, Turkey to Syria–Turkey border, the north, Iraq to Iraq–Syria border, t ...
). In April 2013, a case of wild polio in
Mogadishu Mogadishu, locally known as Xamar or Hamar, is the capital and List of cities in Somalia by population, most populous city of Somalia. The city has served as an important port connecting traders across the Indian Ocean for millennia and has ...
was reported, the first in Somalia since 2007. By October, over 170 cases had been reported in the country, with more cases in neighboring Kenya and the
Somali Region The Somali Region (, , ), also known as Soomaali Galbeed () and officially the Somali Regional State, is a Regions of Ethiopia, regional state in eastern Ethiopia. It is the largest region of Ethiopia. The state borders the Ethiopian regions ...
of Ethiopia. Routine sewage monitoring in 2012 had detected a WPV1 strain of Pakistani origin in
Cairo Cairo ( ; , ) is the Capital city, capital and largest city of Egypt and the Cairo Governorate, being home to more than 10 million people. It is also part of the List of urban agglomerations in Africa, largest urban agglomeration in Africa, L ...
, sparking a major vaccination push there. The strain spread to Israel, where there was widespread environmental detection, but like Egypt, no paralysis cases. It had more severe consequences when it spread to neighboring Syria, with the total number of cases eventually reaching 35, the first outbreak there since 1999. In April 2013, the WHO announced a new $5.5billion, 6-year cooperative plan (called the 2013–18 Polio Eradication and Endgame Strategic Plan) to eradicate polio from its last reservoirs. The plan called for mass immunization campaigns in the three remaining endemic countries, and also dictated a switch to inactivated virus injections, to avoid the risk of the vaccine-derived outbreaks that occasionally occur from use of the live-virus oral vaccine. In 2014, there were 359 reported cases of wild poliomyelitis, spread over twelve countries. Pakistan had the most with 306, an increase from 93 in 2013, which was blamed on Al Qaeda and Taliban militants preventing aid workers from vaccinating children in rural regions of the country. On 27 March 2014, the WHO announced the eradication of poliomyelitis in the South-East Asia Region, in which the WHO includes eleven countries:
Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
,
Bhutan Bhutan, officially the Kingdom of Bhutan, is a landlocked country in South Asia, in the Eastern Himalayas between China to the north and northwest and India to the south and southeast. With a population of over 727,145 and a territory of , ...
,
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korea, Korean Peninsula and borders China and Russia to the north at the Yalu River, Yalu (Amnok) an ...
,
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
,
Maldives The Maldives, officially the Republic of Maldives, and historically known as the Maldive Islands, is an Archipelagic state, archipelagic country in South Asia located in the Indian Ocean. The Maldives is southwest of Sri Lanka and India, abou ...
,
Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...
,
Nepal Nepal, officially the Federal Democratic Republic of Nepal, is a landlocked country in South Asia. It is mainly situated in the Himalayas, but also includes parts of the Indo-Gangetic Plain. It borders the Tibet Autonomous Region of China Ch ...
,
Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...
,
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
, and
Timor-Leste Timor-Leste, also known as East Timor, officially the Democratic Republic of Timor-Leste, is a country in Southeast Asia. It comprises the eastern half of the island of Timor, the coastal exclave of Oecusse in the island's northwest, and ...
. With the addition of this region, the proportion of world population living in polio-free regions reached 80%. The last case of wild polio in the South-East Asia Region was reported in India on 13 January 2011. During 2015, 74 cases of wild poliomyelitis were reported worldwide, 54 in Pakistan and 20 in Afghanistan. There were 32 circulating vaccine-derived poliovirus (cVDPV) cases in 2015. On 25 September 2015, the WHO declared that Nigeria was no longer considered endemic for wild polio virus, with no reported case of wild polio virus having been reported since 24 July 2014. A WPV1 strain not seen in five years resurfaced in Nigeria the following year. The WPV2 virus was declared eradicated in September 2015 as it had not been detected in circulation since 1999, and WPV3 was declared eradicated in October 2019, having last been detected in 2012. However, both types persist as circulating vaccine-derived strains, the product of years of evolution of the attenuated "live" virus (which makes up the oral vaccine) as it transmits from the vaccinated to the unvaccinated and circulates in an under-immunized community.


2016–2020

Because cVDPV2 strains continued to arise from trivalent oral vaccine that included attenuated PV2, during 2016 this vaccine was replaced with a bivalent version lacking WPV2 as well as trivalent injected inactivated vaccine that cannot lead to cVDPV cases. This was expected to prevent new strains of cVDPV2 from arising and allow eventual cessation of WPV2 vaccination. The resulting global use of the injectable vaccine caused shortages, and led the WHO in April 2017 to recommend general use of the fIPV vaccination protocol, involving
subcutaneous injection Subcutaneous administration is the insertion of medications beneath the skin either by injection or infusion. A subcutaneous injection is administered as a bolus (medicine), bolus into the subcutis, the layer of skin directly below the dermis and ...
of a lower dose than used in the standard
intramuscular Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles hav ...
delivery. In 2016 there were 37 reported WPV1 cases, half as many as in 2015, with the majority of the cases in Pakistan and Afghanistan. A small number of additional cases in Nigeria, caused by WPV1, were viewed as a setback, the first being detected there in almost two years, yet the virus had been circulating undetected in regions inaccessible due to the activities of
Boko Haram Boko Haram, officially known as Jama'at Ahl al-Sunna li al-Da'wa wa al-Jihad (), is a self-proclaimed jihadist militant group based in northeastern Nigeria and also active in Chad, Niger, northern Cameroon, and Mali. In 2016, the group spli ...
. There was also a cVDPV1 outbreak in Laos, while new strains of cVDPV2 arose separately in Nigeria's Borno and Sekoto states, and in the Quetta area of Pakistan, collectively causing five cases. In 2017 there were 22 reported WPV1 polio cases with onset of paralysis in 2017, down from 37 in 2016. Eight of the cases were in Pakistan and 14 in Afghanistan, where genetic typing showed repeated introduction from Pakistan as well as local transmission. In Pakistan, transmission of several genetic lineages of WPV1 seen in 2015 had been interrupted by September 2017, though at least two genetic clusters remain. In spite of a significant drop in detected cases in Pakistan, there was an increase in the percentage of environmental samples that test positive for the polio virus, suggesting gaps in identification of infected individuals. In the third country where polio remained endemic, Nigeria, there were no cases, though as few as 7% of infants were fully vaccinated in some districts. An April 2017 spill at a vaccine production facility in the Netherlands only resulted in one asymptomatic WPV2 infection, despite release into the sewer system. Laos was declared free of cVDPV1 in March 2017, but three distinct cVDPV2 outbreaks occurred in the Democratic Republic of the Congo, one of them of recent origin, the other two having circulated undetected for more than a year. Together they caused 20 cases by year's end. In Syria, a large outbreak began at
Mayadin Mayadin (/ALA-LC: ''al-Miyādīn'') is a town in eastern Syria. It is the capital of the Mayadin District, part of the Deir ez-Zor Governorate. Mayadin is about 44 kilometers southeast of Deir ez-Zor. The Euphrates River flows through the town ...
,
Deir ez-Zor Governorate Deir ez-Zor Governorate ( / ALA-LC: ''Muḥāfaẓat Dayr az-Zawr,'' Kurdish'':'' ''Parêzgeha Dêrezor'') is one of the fourteen governorates (provinces) of Syria. It is situated in eastern Syria, bordering Iraq. It has an area of 33,060 k ...
, a center of fighting in the Syrian Civil War, and also spreading to neighboring districts saw 74 confirmed cases from a viral strain that had circulated undetected for about two years. Circulation of multiple genetic lines of cVDPV2 was also detected in Banadir province, Somalia, but no infected individuals were identified. WHO's Strategic Advisory Group of Experts on Immunization recommended that cVDPV2 suppression be prioritized over targeting WPV1, and according to protocol OPV2 is restricted to this purpose. There were 33 reported WPV1 paralysis cases with an onset of paralysis in 2018 – 21 in Afghanistan and 12 in Pakistan. Polio in Pakistan resurged in the latter part of the year, due in part to the rates of parental refusal for vaccination increasing, with wild poliovirus detected in 20% of the year's environmental samples. In Afghanistan different strains were largely responsible for the cases in the northeast and south of the country. In Nigeria, the third country classified as having endemic transmission, security concerns continued to limit access to some areas of the country, though migration and novel vaccination approaches would reduce the number of unreached children. The nation passed two full years without a detected wild-virus case, though elimination of WPV transmission could not be confirmed.Cases caused by vaccine-derived poliovirus were reported in seven countries in 2018, with over 100 total cases, representing nine strains of cVDPV. In the Democratic Republic of the Congo, one of the outbreaks of cVDPV2 first detected in 2017 caused no additional cases, but suppression of the other two with OPV2 proved insufficient: not only did they continue, but the vaccination efforts gave rise to a novel cVDPV2 outbreak. The country experienced a total of 20 cases in 2018. Two separate cVDPV2 outbreaks in northern Nigeria produced 34 cases, as well as giving rise to 10 cases in the neighboring Niger. In Somalia, cVDPV2 continued to circulate, causing several polio cases and detected in environmental samples from as far as
Nairobi Nairobi is the Capital city, capital and largest city of Kenya. The city lies in the south-central part of Kenya, at an elevation of . The name is derived from the Maasai language, Maasai phrase , which translates to 'place of cool waters', a ...
, Kenya. This virus, along with newly detected cVDPV3, caused twelve total cases in the country, including one patient infected by both strains. The large number of children residing in areas inaccessible to health workers represent a particular risk for undetected cVDPV outbreaks. A cVDPV2 outbreak in Mozambique resulted in a single case. Response to the Syrian cVDPV2 outbreak continued into 2018, and virus transmission was successfully interrupted. In
Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...
, a cVDPV1 strain arose, causing twenty-six polio cases across nine provinces, while a single diagnosed cVDPV1 case in neighboring
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
resulted from a distinct outbreak. In 2019 there were 176 WPV1 paralysis cases detected: 29 in Afghanistan and 147 in Pakistan. In particular, in Pakistan the number of cases was surging and cross-border migration played a role in polio transmission between the two countries. While itself problematic, this also fostered a dangerous false narrative in both nations, blaming the other for the presence and spread of polio in their own country. Environmental sampling in Pakistan showed the virus' presence in eight urban areas, a setback officials attributed primarily to vaccine refusal. Opponents to vaccination in Pakistan launched a series of attacks in April that left a vaccinator and two security men dead, while false rumors and hoax videos reporting vaccine toxicity also disrupted vaccination efforts there. Wild poliovirus of Pakistani origin also spread to Iran where it was detected in several environmental samples. Overall, the eradication efforts in Pakistan and Afghanistan have been characterized as having become a "horror show", undermined by "public suspicion, political infighting, mismanagement and security problems". In the third remaining country in which polio was classified as endemic, Nigeria, wild poliovirus has not been detected since October 2016, and levels of AFP surveillance are sufficient, even in security-compromised regions, to suggest transmission of WPV may have been interrupted. Global WPV3 eradication was certified in October 2019, the virus not having been seen since 2012. In addition to the WPV resurgence in Pakistan and Afghanistan, 2019 saw a resurgence of cVDPV, with 378 cases. The majority of cases were caused by cVDPV2 strains that were able to arise or spread as a consequence of the withdrawal of the PV2 strain from the standard vaccination regimen. Previous cVDPV2 outbreaks in Nigeria, the Democratic Republic of Congo, and Somalia continued into 2019 and spread to neighboring countries, while several countries experienced new outbreaks. In addition to eighteen reported paralysis cases in Nigeria, the cVDPV2 outbreaks there spread to Benin, Burkina Faso, Chad, Ghana, Niger, and Togo, while the virus was also detected in environmental samples from Cameroon and Ivory Coast. Somalia's continuing outbreaks caused a half-dozen cases there and in neighboring Ethiopia, with a separate Ethiopia outbreak adding one case. The Democratic Republic of the Congo had numerous new and continuing outbreaks, producing more than 80 cases, while multiple new cVDPV2 outbreaks in Angola and the Central African Republic resulted in more than a hundred cases. Individual new outbreaks of cVDPV2 also caused more than a dozen paralysis cases each in Pakistan and the Philippines, while smaller outbreaks struck Chad, China, and Zambia. A separate cVDPV1 outbreak in the Philippines also caused cases in Malaysia, where cVDPV2 of Filipino origin was also detected in environmental samples, while additional cVDPV1 outbreaks caused six cases in Myanmar and one case in Yemen. In March 2020, the GPEI announced polio eradication resources were being redeployed against the
COVID-19 pandemic The COVID-19 pandemic (also known as the coronavirus pandemic and COVID pandemic), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), began with an disease outbreak, outbreak of COVID-19 in Wuhan, China, in December ...
, recognizing that this would adversely affect its efforts at eradicating polio. All vaccination efforts, both routine and targeted, were postponed for several months, with staff reassigned to COVID-19 control. Subsequent statistical analysis indicated that the COVID pandemic resulted in decreases of more than 30% globally in both AFP and environmental surveillance, with only 23 of 43 priority countries meeting their surveillance targets for 2020. Additional challenges were a conspiracy theory circulating on social media claiming that the polio vaccine contained coronavirus, and moves by President Donald Trump of the United States to cut funding for the World Health Organization. Nigeria was removed from the list of countries with endemic wild poliovirus in June 2020, four years after the last recorded case in the Northern State of Borno in 2016. Two months later, the World Health Organization declared the African continent free of wild poliovirus. This certification came after extensive assessments of the certifications of National Polio Certification Commissions (NCCs) and confirmation that at least 95% of Africa's population had been immunised. WHO Director-General Tedros Adhanom called it a "great day... but not the end of polio", as there remain major continuing outbreaks of vaccine-derived poliovirus in West Africa and Ethiopia in addition to wild cases in Afghanistan and Pakistan. Over 1000 cases caused by both continuing and novel outbreaks of cVDPV2 were reported in 2020 across twenty-four countries, with 31 additional cases of cVDPV1, and environmental detections in several additional countries with no diagnosed polio cases. While in the past cVDPV outbreaks tended to remain localized, significant international spread of these strains was observed.


2021

In 2021, there were just six confirmed cases of wild poliovirus — one in Pakistan, four in Afghanistan, and one in Malawi. 2021 saw a partial recovery from the challenges to monitoring brought on by the COVID pandemic, with 74% of high-priority countries meeting surveillance targets, an improvement of over 20% from the previous year. March 2021 also saw the first use of the modified nOPV2 vaccine in selected countries, engineered to allow vaccination against strain2 poliovirus without the frequent spawning of cVDPV2 seen with the original OPV2. Full rollout was not expected until 2023. Despite previous resistance to eradication efforts, after their takeover of Afghanistan in 2021 the
Taliban , leader1_title = Supreme Leader of Afghanistan, Supreme leaders , leader1_name = {{indented plainlist, * Mullah Omar{{Natural Causes{{nbsp(1994–2013) * Akhtar Mansour{{Assassinated (2015–2016) * Hibatullah Akhundzada (2016–present) ...
agreed to allow United Nations healthcare workers to carry out door-to-door vaccination nationwide for the first time in three years, including a commitment to allowing women to participate in the effort, and to provide safety guarantees to eradication staff. Pakistan's lone case dated from January, but the virus continued to be detected in environmental samples through December, and was present in most provinces of the country during the year. The case in Malawi, the country's first in almost three decades and the first in Africa in five years, was seen as a significant setback to the eradication effort. Based on similarity to a strain last detected in Pakistan in 2019, it is thought that WPV1 has been circulating undetected in the country for some time. In 2021, reported cVDPV2 cases declined to 685 across 22 countries, over half occurring in Nigeria. The virus was also found in environmental samples or in those from symptom-free people in several additional African and Asian nations without reported cases. An analysis of cVDPV2 strains from 2020 and the first half of 2021 attributed them to 38 distinct emergences, representing a mix of novel strains and previously detected strains that continued to circulate, while several previously circulating strains were no longer found. 14 cases of cVDPV1 were identified in Madagascar and 3 in Yemen. No cases of cVDPV3 were observed, though it was detected in environmental samples from China, Israel, and its adjacent occupied territories.


2022

In 2022, there were 30 confirmed cases of WPV1 reported to WHO, with two and 20 cases in Pakistan and Afghanistan respectively, while eight non-endemic cases were recorded in Mozambique, the first cases in the country since 1992. The Mozambique cases derived from the strain of Pakistani origin that caused two confirmed cases in Malawi in 2021. The cases in Pakistan were the first seen in the country in 15 months, though the virus had been detected in environmental samples during the intervening period. The residual effects of the COVID-19 pandemic continued to be a cause for concern, due to an increased risk of undetected outbreaks due to COVID's interference with routine health care, disease detection, and childhood vaccinations, as well as a concern that an increased fear of vaccines, caused at least in part by politicization of vaccination and bad governance during the pandemic, may result in a general pattern of undervaccination, including for polio. In Pakistan, a contributing factor to the resurgence of wild virus cases in the country has been threats of violence both from those with anti-vaccine sentiment and from religious extremists. A vaccination worker was assassinated in March 2022, and a vaccinator and two accompanying police officers providing security for a door-to-door vaccination campaign were murdered in June. However, the situation had improved compared to previous years as the government and law-enforcement increased their focus. By October 2022, endemic transmission was restricted to seven districts in southern
Khyber Pakhtunkhwa Khyber Pakhtunkhwa (; ; , ; abbr. KP or KPK), formerly known as the North West Frontier Province (NWFP), is a Administrative units of Pakistan, province of Pakistan. Located in the Northern Pakistan, northwestern region of the country, Khyber ...
, and the number of circulating genetic clusters was down to one, from eleven in 2020. The situation improved in Afghanistan as well, as between 2021 and 2022 the country became significantly more peaceful as the government consolidated their control, though with remaining pockets of violence. Vaccine-derived cases continue to circulate, particularly in the African and Eastern Mediterranean WHO regions. Concern is focused on Ukraine, where cVDPV had been detected in fall 2021, vaccination efforts were halted due to the Russian invasion, and on poor quality surveillance extant in Southeast Africa 684 confirmed cVDPV2 cases were seen across twenty countries during 2022, in addition to 189 cases of cVDPV1 and one case of cVDPV3 in Israel. The first case since 2013 was reported in the United States, tied to cVDPV2 strains found in Israel and the United Kingdom. In Burundi and the Democratic Republic of the Congo, two outbreaks of cVDPV2 that caused a combined seven cases were identified as having a link to the nOPV2 vaccine, the first outbreaks with ties to nOPV2 after its initial deployment in 2021; according to an assessment reported by the GPEI, an estimated 30–40 additional outbreaks of cVDPV2 would have occurred from March 2021 – March 2023 without the nOPV2 rollout. Vaccine-derived viral strains were also detected in environmental samples from a number of additional countries without diagnosed cases. From February to May, traces of cVDPV2 were discovered in sewage in London, United Kingdom. This led the United Kingdom to declare a "national incident". However, authorities have said that the risk to the general public is "extremely low", and no cases have been reported.


2023

Twelve cases of WPV1 have been reported in 2023, six in Afghanistan and Pakistan each. Additionally, 187 positive environmental samples were reported in those countries. There have been 391 confirmed cases of cVDPV2 reported to the WHO in 2023, across 22 countries, nineteen of which lie in
Sub-Saharan Africa Sub-Saharan Africa is the area and regions of the continent of Africa that lie south of the Sahara. These include Central Africa, East Africa, Southern Africa, and West Africa. Geopolitically, in addition to the list of sovereign states and ...
, with only a handful of cases in Indonesia, Yemen, and Israel being the exception. cVDPV1 is now concentrated in three countries, 105 cases in the Democratic Republic of the Congo, 24 in Madagascar and four in Mozambique. No cVDPV3 virus has been detected for two years now. The Independent Monitoring Board of the GPEI in its September 2023 Report mentioned a continued, geographically restricted, endemic transmission in the east of Afghanistan and in the southern districts of Pakistan's
Khyber Pakhtunkhwa Khyber Pakhtunkhwa (; ; , ; abbr. KP or KPK), formerly known as the North West Frontier Province (NWFP), is a Administrative units of Pakistan, province of Pakistan. Located in the Northern Pakistan, northwestern region of the country, Khyber ...
province. Only one wild polio genetic cluster remains in Afghanistan in a much improved immunity (>90%) of the population. Levels of access in the country are the best they have been since 2018. However, a large pool of unvaccinated children remain in the Kandahar province potentially leading to a large outbreak, if the virus reappears there. In Pakistan, they estimate that the long-standing and intractable poliovirus circulation in most of the traditional endemic reservoirs has been eliminated. However, a positive environmental probe in
Karachi Karachi is the capital city of the Administrative units of Pakistan, province of Sindh, Pakistan. It is the List of cities in Pakistan by population, largest city in Pakistan and 12th List of largest cities, largest in the world, with a popul ...
, after no cases for over a year, raised concerns about the vaccination campaign quality in Pakistan. The report found it was highly likely that the goal of interrupting wild poliovirus transmission in 2023 would be missed and it was certain that ending transmission of vaccine-derived poliovirus will not be possible this year.


2024

there have been 99 reported cases of WPV1 with 74 from Pakistan and 25 from Afghanistan. Additionally, 649 positive environmental samples have been collected in Pakistan and 119 in Afghanistan. 297 cases of cVDPV2 cases have been found across twenty different countries, all of which are in
Sub-Saharan Africa Sub-Saharan Africa is the area and regions of the continent of Africa that lie south of the Sahara. These include Central Africa, East Africa, Southern Africa, and West Africa. Geopolitically, in addition to the list of sovereign states and ...
except for Algeria in
Northern Africa North Africa (sometimes Northern Africa) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region. However, it is sometimes defined as stretching from the Atlantic shores of t ...
, Indonesia in
Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
, and Yemen and Palestine in
West Asia West Asia (also called Western Asia or Southwest Asia) is the westernmost region of Asia. As defined by most academics, UN bodies and other institutions, the subregion consists of Anatolia, the Arabian Peninsula, Iran, Mesopotamia, the Armenian ...
. In addition seventeen countries have had positive environmental samples of cVDPV2 but no confirmed cases: Bahrain, Djibouti, Egypt, Equatorial Guinea, Finland, Gambia, Germany, Ghana, Kenya, Mozambique, Poland, Senegal, Sierra Leone, Spain, Uganda, United Kingdom and Zimbabwe. France had one positive environmental sample of cVDPV3. Ten cVDPV1 cases have been detected in the Democratic Republic of the Congo and one in Mozambique. After one and a half years without any cases, cVDPD3 has reappeared with four new cases in Guinea between September and November.


2025

there have been 13 reported cases of WPV1 with 11 from Pakistan and 2 from Afghanistan. Additionally, 250 positive environmental samples have been collected in Pakistan and 30 in Afghanistan. 70 cases of cVDPV2 have been found across ten different countries, all of which are in Sub-Saharan Africa with the exception of Yemen. In addition seven countries from Africa, three from Western Europe, two from West Asia and one country from South East Asia have had positive environmental samples of cVDPV2 but no confirmed cases: Algeria, Cameroon, Central African Republic, Côte d'Ivoire, Germany, Israel, Palestine, Papua New Guinea, Poland, Senegal, Somalia, United Kingdom, and Tanzania. There have been no cases of cVDPV1 so far this year. cVDPV1 has last been detected in September 2024 in the Democratic Republic of Congo. cVDPD3 has reappeared in March 2025 with two cases in Guinea after the last one in November 2024.


See also

* * *
Global Polio Eradication Initiative The Global Polio Eradication Initiative is an initiative created in 1988, just after the World Health Assembly resolved to eradicate the disease poliomyelitis. Led by the World Health Organization, it is the largest international public health ...
* '' The Final Inch'', a 2009 documentary film about the eradication effort *
List of diseases eliminated from the United States This is a list of diseases known (or declared) to have been eliminated from the United States, either permanently or at one time. (" Elimination" is the preferred term for "regional eradication" of a disease; the term " eradication" is reserved for ...
*
Mathematical modelling of infectious disease Mathematical models can project how infectious diseases progress to show the likely outcome of an epidemic (including Plant disease forecasting, in plants) and help inform public health and plant health interventions. Models use basic assumptions ...
* Polio in Pakistan *
Population health Population health has been defined as "the health outcomes of a group of individuals, including the distribution of such outcomes within the group". It is an approach to health that aims to improve the health of an entire human population. It ha ...
* 2024 Gaza Strip polio outbreak


References


Further reading

*


External links

* {{PHEIC Health campaigns Infectious diseases with eradication efforts Polio Public health emergencies of international concern Vaccination