Poliomyelitis eradication

A child receives oral polio vaccine during a 2002 campaign to immunize children in India.

Poliovirus

A public health effort to eliminate all cases of poliomyelitis (polio) infection around the world, begun in 1988 and led by the World Health Organization (WHO), UNICEF and the Rotary Foundation,^[1] has reduced the number of annual diagnosed cases from the hundreds of thousands to fewer than 100 in 2015.^[2] Of the three strains of the polio virus, the last recorded wild case of type 2 was in 1999. The last recorded case of type 3 was on 11 November 2012. All reported cases since 11 November 2012 have been of type 1. If polio is the next disease to be successfully eradicated, this will represent only the third time this has ever been achieved, after smallpox^[3] and rinderpest.^[4] The goal of eradicating polio worldwide has attracted international and media attention, with a reduction of some 99% of cases in the last quarter of the 20th century. The first 10 years of the 21st century saw only erratic progress in further reducing the number of cases, which led to getting rid of the last 1% being described as "like trying to squeeze Jell-O to death".^[5] Since 2011 incidence rates of the disease have dramatically reduced, and with large reductions continuing through to 2015, hopes for eliminating polio have been rekindled. India is the latest country to have officially stopped transmission of polio—with its last reported case in 2011.^[6] Only 2 countries remain where the disease is endemic—Afghanistan and Pakistan. Nigeria's last reported wild case was 24 July 2014, and the WHO declared it no longer to have endemic wild polio on 25 September 2015. The number of cases reported in 2015 is less than a quarter of each of the preceding three years.^[7]

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,^[8] as extinction of poliovirus, such that the infectious agent no longer exists in nature or in the laboratory,^[9] as control of an infection to the point at which transmission of the disease ceased within a specified area,^[8] and as reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.^[10]

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.^[11] 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; 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 reservoir and cannot amplify in the environment.

Strategy

The most important step in eradication of polio is interruption of endemic transmission of poliovirus. Stopping polio transmission has been pursued through a combination of routine immunization, supplementary immunization campaigns and surveillance of possible outbreaks. The four key strategies outlined by the World Health Organization for stopping polio transmission are:^[12]

1. High infant immunization coverage with four doses of oral polio vaccine (OPV) in the first year of life in developing and endemic countries, and routine immunization with OPV and/or IPV elsewhere.
2. Organization of "national immunization days" to provide supplementary doses of oral polio vaccine to all children less than five years of age.
3. Active surveillance for wild 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 and reduced muscle tone without other obvious cause (e.g., trauma). AFP is also associated with a number of other pathogenic agents including enteroviruses, echoviruses, and adenoviruses, among others.^[13] among children less than fifteen years of age.
4. Targeted "mop-up" campaigns once wild poliovirus transmission is limited to a specific focal area.

Vaccination

Oral polio vaccine is highly effective and inexpensive (about US$0.10 per dose, or US$0.30 per child^[14]) and its availability has bolstered efforts to eradicate polio. A study carried out in an isolated Eskimo village showed that antibodies produced from subclinical wild virus infection persisted for at least 40 years.^[15] Because the immune response to oral polio vaccine is very similar to natural polio infection, it is expected that oral polio vaccination provides similar lifelong immunity to the virus.^[16][17]

Contact immunity to polio can occur when attenuated poliovirus derived from the oral polio vaccine is excreted, and infects and indirectly vaccinates unvaccinated individuals.^[18]

Herd immunity

Polio vaccination is also important in the development of herd immunity.^[19] For polio to occur in a population, there needs to be an infecting organism (poliovirus), a susceptible human population, and a cycle of transmission. Poliovirus is transmitted only through person-to-person contact and the transmission cycle of polio is from one infected person to another person susceptible to the disease, and so on.^[18] If the vast majority of the population is immune to a particular agent, the ability of that pathogen 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, then the pathogen will eventually die off.

When many hosts are vaccinated, especially simultaneously, the transmission of wild virus is blocked, and the virus is unable to find another susceptible individual to infect. Because poliovirus can only survive for a short time in the environment (a few weeks at room temperature, and a few months at 0–8 °C (32–46 °F)) without a human host the virus dies out.^[20]

Herd immunity is an important supplement to vaccination. Among those individuals who receive oral polio vaccine, only 95 percent will develop immunity.^[21] That means five of every 100 given the vaccine will not develop any immunity and will be susceptible to developing polio. According to the concepts of herd immunity this population whom the vaccine fails, are still protected by the immunity of those around them. Herd immunity can only be achieved when vaccination levels are high.^[19] It is estimated that 80–86 percent of individuals in a population must be immune to polio for the susceptible individuals to be protected by herd immunity.^[19] If routine immunization were stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.^[22]

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 of live (attenuated) vaccines in extremely hot or remote areas. The oral polio vaccine must be kept at 2 to 8 °C (36 to 46 °F) for vaccination to be successful.^[16]

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, they 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, inadequately resourced health facilities, also posed problems, as well as technical issues with the vaccine. In India, the major challenge appeared to be the high efficiency of transmission within the populations of Bihar and Uttar Pradesh states, set against the low (~80% after three doses against type 1) seroconversion response seen from the vaccine. In Nigeria, meanwhile, 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 also played a role. Finally, in those countries where international spread from endemic countries had resulted in transmission becoming re-established—namely Angola, Chad, and South Sudan, the key issues identified were underdeveloped health systems and low routine vaccine coverage, although low resources committed to Angola and South Sudan for the purpose of curtailing the spread of polio and climatic factors were also identified as playing a role.^[23]

Two additional challenges are found in unobserved polio transmission and in vaccine-derived poliovirus. In 99% of infections, polio is a mild condition that causes very few symptoms^[24] and most infected people are unaware that they carry the disease, allowing polio to spread widely before cases are seen.^[25] And since 2000, there have been a number of outbreaks of circulating vaccine-derived poliovirus, following mutations or recombinations in the attenuated strain used for the oral polio vaccine, which have raised the necessity of eventually switching to the more expensive inactivated polio vaccine.^[26] The risk of vaccine-derived polio will persist long after the switch to inactivated vaccine, since a small number of chronic excretors continue to produce active virus for years (or even decades) after their initial exposure to the oral vaccine.^[27]

In a 2012 interview with Pakistani newspaper Dawn, Dr. Hussain A. Gezari, WHO's special envoy on global polio eradication and primary healthcare, gave his views on obstacles to eradication. He said the biggest hurdle in making Pakistan polio-free was holding district health officials properly accountable—in national eradication campaigns officials had hired their own relatives, even young children. "How do you expect a seven-year-old thumb-sucking kid to implement a polio campaign of the government," said Dr Gezari. He 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."^[28]

Opposition and aid worker killings

One factor contributing to the continued circulation of polio immunization programs has been opposition in some countries.^[29] In Pakistan and Afghanistan, the Taliban have issued fatwas against polio vaccination.^[30][31]

After the September 11 attacks, a myth arose in Pakistan that the United States was using immunization campaigns to sterilize the local population. Health officials tried to dispel this story, but their efforts, in the opinion of Heidi Larson, writing in The Guardian, were marred by the Central Intelligence Agency (CIA), when it conducted a fake Hepatitis B immunization campaign in Bin Laden's residence in Bilal Town at Abbottabad with the help of Dr. Shakil Afridi.^[32] The intention of the campaign was to confirm Osama bin Laden's presence in the city by obtaining DNA samples from children suspected of being his.^[33] In a letter written to CIA director Leon Panetta, 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.^[34] Pakistan reported the world's highest number of polio cases (198)^[28][35] in 2011.^[36] In early 2012, some parents refused to get their children vaccinated in Khyber Pakhtunkhwa and in the Federally Administered Tribal Areas (FATA) but religious refusals in the rest of the country had "decreased manifold".^[28]

Even with the express support of political leaders, polio workers have been kidnapped, beaten, and assassinated.^[29] In February 2007, physician Abdul Ghani, who was in charge of polio immunizations in a key area of disease occurrence in northern Pakistan, was killed in a terrorist bombing.^[37] In 2012, there was the killing of a polio worker in Gadap in October. In December 2012, a 3-day vaccination campaign sponsored by the United Nations agencies the World Health Organization and UNICEF in Pakistan was suspended following the murder of 9 vaccination workers.^[38]

The killing of polio workers seen the previous year continued in 2013. Seven clinic workers whose duties included vaccination were killed in Swabi, Pakistan on New Year's Day. The Pakistani government began providing police and paramilitary protection to a renewed vaccination campaign,^[39] but amid worries that this would inspire hostility, some escorts have been refused. Both escorting officers^[40][41][42] and polio workers continue to be killed in Pakistan, where vaccination has been said to violate Islamic law.^[43][44] In February a pair of similar attacks in Nigeria killed nine female polio vaccinators following a local cleric's condemnation of vaccination.^[45] The security situation in Afghanistan improved in May when the Afghani Taliban announced it would support polio eradication, pledging to do nothing to hinder the campaign as long as no foreigners were involved in the vaccinations.^[46] In December 2013, three polio workers were killed in northwest Pakistan and three more were killed in Karachi in January 2014.^[47]

Progress and setbacks

International Wild Poliovirus Cases by Year
Year	Estimated	Recorded
1975	—	49,293
1980	400,000	52,552
1985	—	38,637
1988	350,000	35,251
1990	—	23,484
1993	100,000	10,487
1995	—	7,035
2000	—	719
2001	—	483
2002	—	1,918
2003	—	784
2004	—	1,255
2005	—	1,979
2006	—	1,997
2007	—	1,315
2008	—	1,651
2009	—	1,604
2010	—	1,352
2011	—	650
2012	—	223
2013	—	416
2014	—	359
2015	—	74
References: 2000 to 2015: WHO;[48] other data[16][49][50][51][52][53]

Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries.^[21] Czechoslovakia became the first country in the world to scientifically demonstrate nationwide eradication of poliomyelitis in 1960.^[54] In 1962—just one year after Sabin's oral polio vaccine (OPV) was licensed in most industrialized countries—Cuba 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.^[55] The Pan American Health Organization (PAHO), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the Americas in 1985.^[56]

Much of the work towards eradication was documented by Brazilian photographer Sebastião Salgado, as a UNICEF Goodwill Ambassador, in the book The End of Polio: Global Effort to End a Disease.^[57]

1988–1991

In 1988, the World Health Organization, together with Rotary International, UNICEF, and the U.S. Centers for Disease Control and Prevention passed the Global Polio Eradication Initiative, with the goal of eradicating polio by the year 2000. The Initiative was inspired by Rotary International's 1985 pledge to raise $120 million toward immunising all of the world's children against the disease.^[56] The last case of wild poliovirus poliomyelitis in the Americas was reported in Peru, August 1991.^[56]

1994–2000

On 20 August 1994 the Americas were certified as polio-free.^[58] This achievement was a milestone in efforts to eradicate the disease.

In 1994 the Indian Government launched the Pulse Polio Campaign to eliminate polio. The current campaign involves annual vaccination of all children under age five.^[59]

In 1995 Operation MECACAR (Mediterranean, Caucasus, Central Asian Republics and Russia) were launched; National Immunization Days were coordinated in 19 European and Mediterranean countries.^[60] In 1998, Melik Minas of Turkey became the last case of polio reported in Europe.^[61] In 1997 Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region.^[62] In 2000 the Western Pacific Region (including China) was certified Polio-free.^[62]

In October 1999, the last isolation of type 2 poliovirus occurred in India. This type of poliovirus was declared eradicated.^[21][63]

Also in October 1999, The CORE Group—with funding from the United States Agency for International Development (USAID)—launched its effort to support national eradication efforts at the grassroots level. The CORE Group initiated this initiative in Bangladesh, India and Nepal in South Asia, and in Angola, Ethiopia and Uganda in Africa.^[64]

2001–2004

Disability-adjusted life year for poliomyelitis per 100,000 inhabitants in 2004

no data   <0.3   0.3–0.75   0.75–1.2   1.2–1.65   1.65–2.1   2.1–2.55

2.55–3   3–4   4–5   5–7.5   7.5–10   >10

By 2001, 575 million children (almost one-tenth the world's population) had received some 2 billion doses of oral polio vaccine.^[65] The World Health Organization announced that Europe was polio-free on June 21, 2002, in the Copenhagen Glyptotek.^[66]

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 accounted for nearly two-thirds of total worldwide cases reported.^[67] (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, 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.^[68] On June 30, 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.^[56] By 2006, this ban would be blamed for 1,500 children being paralyzed and had cost $450 million for emergency activities. In addition to the rumors of sterility and the ban by Nigeria's Kano state, civil war and internal strife in the Sudan and Côte d'Ivoire have complicated WHO's polio eradication goal. In 2004, almost two-thirds of all the polio cases in the world occurred in Nigeria (760 out of 1,170 total).

2005

Countries with polio cases in 2005

There were 1,979 cases of wild poliovirus (excludes vaccine-derived polio viruses) in 2005.^[69] Most remaining polio infections were located in two areas: the Indian subcontinent and Nigeria.

Eradication efforts in the Indian sub-continent have met with a large measure of success. Using the Pulse Polio campaign to increase polio immunization rates, India recorded just 66 cases in 2005, down from 135 cases reported in 2004, 225 in 2003, and 1,600 in 2002.^[70]

Yemen, Indonesia and Sudan, countries that had been declared polio-free since before 2000, each reported hundreds of cases—probably imported from Nigeria.^[71] On May 5, 2005, news reports broke that a new case of polio was diagnosed in Java, Indonesia, 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.^[72]

The first case of the polio outbreak in Sudan was detected in May 2004. The reemergence of polio led to stepped up vaccination campaigns. In the city of Darfur, 78,654 children were immunized and 20,432 more in southern Sudan (Yirol and Chelkou).^[73]

In the United States on September 29, 2005, the Minnesota Department of Health identified the first occurrence of vaccine derived polio virus (VDPV) transmission in the United States since OPV was discontinued in 2000. The poliovirus type 1 infection occurred in an unvaccinated, immunocompromised infant girl aged 7 months (the index patient) in an Amish community whose members predominantly were not vaccinated for polio.^[74]

2006–2010

In 2006 only four countries in the world (Nigeria, India, Pakistan and Afghanistan) were reported to have endemic poliomyelitis. 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.^[69] Nigeria accounted for the majority of cases (1,122 cases) but India reported more than ten times more cases this year 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 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.^[75] (See: Map of reported polio cases in 2006)

In 2007 there were 1,315 cases of poliomyelitis reported worldwide.^[69] Over 60% of cases (874) occurred in India; while 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.^[71] Turai Yar'Adua, wife of recently elected Nigerian president Umaru Yar'Adua, made the eradication of polio one of her priorities. Attending the launch of immunization campaigns in Birnin Kebbi in July 2007, Turai Yar'Adua urged parents to vaccinate their children and stressed the safety of oral polio vaccine.^[76]

In July 2007, a student traveling from Pakistan imported the first polio case to Australia in over 20 years.^[77] Other countries with significant numbers of wild polio virus cases include the Democratic Republic of the Congo, which reported 41 cases, Chad with 22 cases, and Niger and Myanmar, each of which reported 11 cases.^[69]

In 2008, 19 countries reported cases and the total number of cases was 1,652. Of these, 1,506 occurred in the four endemic countries and 146 elsewhere. The largest number were in Nigeria (799 cases) and India (559 cases): these two countries contributed 82.2 percent of all cases. Outside endemic countries Chad reported the greatest number (37 cases).^[69]

In 2009, a total of 1,606 cases were reported in 23 countries. 1,256 of these were in the four endemic countries, with the remaining 350 in 19 sub-Saharan countries with imported cases or re-established transmission. Once again, the largest number were in India (741) and Nigeria (388).^[69] All other countries had less than one hundred cases: Pakistan had 89 cases, Afghanistan 38, Chad 65, Sudan 45, Guinea 42, Angola 29, Côte d'Ivoire 26, Benin 20, Kenya 19, Niger 15, Central African Republic 14, Mauritania 13 and Sierra Leone and Liberia both had 11. The following countries had single digit numbers of cases: Burundi 2, Cameroon 3, the Democratic Republic of the Congo 3, Mali 2, Togo 6 and Uganda 8.

According to figures updated in April 2012, the World Health Organization reports that there were 1,352 cases of wild polio in 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). 460 cases (34% of the global total) were reported from an acute outbreak in Tajikistan, which was associated with a further 18 cases across Central Asia (Kazakhstan and Turkmenistan) and the Russian Federation, with the most recent case from this region being reported from Russia the 25th September. These were the first cases in the WHO European region since 2002. 441 cases (30% of the global total) were reported from an outbreak in the Republic of Congo (Brazzaville). At least 179 deaths were associated with this outbreak, which is believed to have been an importation from the ongoing type 1 outbreak in Angola (33 cases in 2010) and the Democratic Republic of the Congo (100 cases).^[69][78]

Reported Polio Cases in 2011[78][79]
Country	Wild Cases	Circulating Vaccine- derived Cases	Transmission Status
Pakistan	198	0	endemic
Chad	132	0	re-established
DRC	93	11	importation
Afghanistan	80	1	endemic
Nigeria	62	33	endemic
Côte d'Ivoire	36	0	importation
China	21	0	importation
Mali	7	0	importation
Angola	5	0	re-established
Niger	5	1	importation
Central African Republic	4	0	importation
Guinea	3	0	importation
Republic of the Congo	1	0	importation
Gabon	1	0	importation
India	1	0	endemic
Kenya	1	0	importation
Somalia	0	9	cVDPV only
Yemen	0	9	cVDPV only
Mozambique	0	2	cVDPV only
Total	650	66

2011

In 2011, cases were reported in the four endemic countries—Pakistan, Afghanistan, Nigeria and India—as well as in the Democratic Republic of Congo, Chad, Angola, Mali, Côte d'Ivoire, Burkina Faso, the Republic of Congo (Brazzaville), Niger, and Gabon. Almost 87 percent of all cases seen this year came from five countries: Pakistan, Chad, the Democratic Republic of the Congo, Afghanistan and Nigeria. In India, only 1 case of wild poliovirus was reported—a remarkable feat in a country that in many recent years has had a plurality or majority of the world's polio cases.^[80]

Since the start of 2010 there had been 14 outbreaks of polio, several continuing into 2011. Amid political instability, Côte d'Ivoire reported 36 cases of type 3 polio as part of an ongoing outbreak, with type 3 cases also in neighboring Mali and Guinea. Polio transmission recurred in Angola, Chad and the Democratic Republic of the Congo. Kenya reported its first case since 2009, while China reported 21 cases, mostly among the Uyghurs of Hotan prefecture, Xinjiang, the first cases since 1994. Although the situation in Northern Nigeria improved, concerns exist about further outbreaks there because of its central location.

The situation in Pakistan is complex. The lowest number of cases reported in one year was 32 in 2007. In 2011, Pakistan reported 198 cases. The remaining focuses lie in three parts of Pakistan: Balochistan Province, Karachi and the Federally Administered Tribal Areas.^[81] About 25% of children in Karachi are unvaccinated against polio; in Balochistan ~50% are unvaccinated. In contrast in Afghanistan the unvaccinated rate is ~10%. The difficulty in Pakistan appears to be a lack of trust in the health workers trying to vaccinate the children, fueled partly by the CIA using fake vaccination campaigns as a cover to gather DNA samples from Osama Bin Laden's relatives.^[82]

At end of 2011 the WHO recorded a total of 650 cases worldwide.^[83] 310 of these were considered to be part of outbreaks. 16 countries recorded cases. Pakistan had the greatest number (198). Six other countries recorded numbers in double digits: Chad: 132 cases; Democratic Republic of Congo: 93; Afghanistan: 80; Nigeria: 61; Côte d'Ivoire: 36; and China: 21. The remaining countries were: Mali: 7; Angola: 5; Niger: 5; Central African Republic: 4; Guinea: 3; Congo: 1; Gabon: 1; India: 1; and Kenya: 1.

2012

Polio free

Reported Polio Cases in 2012[78][79]
Country	Wild Cases	Circulating Vaccine- derived Cases	Transmission Status
Nigeria	122	9	endemic
Pakistan	58	16	endemic
Afghanistan	37	9	endemic
Chad	5	12	re-established
Niger	1	0	importation
DRC	0	17	cVDPV only
Kenya	0	3	cVDPV only
Yemen	0	2	cVDPV only
China	0	2	cVDPV only
Somalia	0	1	cVDPV only
Total	223	71

Several countries surpassed a year since their most recent reported case of polio. Most notably, the WHO reported that on January 13, India completed its first polio-free year and is now polio-free,^[84] leaving only three countries worldwide that have remained afflicted by endemic poliomyelitis. Other countries that in 2012 surpassed a year since a reported case the previous year were Gabon and Congo (January), Mali (June), Côte d'Ivoire, Angola and Kenya (July) and Guinea (August), China (October), and Central African Republic and the Democratic Republic of Congo (December). All those previously-infected countries did not report a case in 2012. Reported cases were limited to five countries, Nigeria, Pakistan, Afghanistan, Chad and Niger, four of which had fewer cases compared to 2011.^[7]

Africa

Nigeria remains the only polio-endemic country in Africa. By the end of the year, the number of confirmed cases in Nigeria was 122, of which 19 were type 3, well in excess of the 62 total cases reported in 2011. 90% of these cases were reported from eight persistently endemic northern states: Borno, Jigawa, Kano, Katsina, Kebbi, Sokoto, Yobe and Zamfara. The situation in northern Nigeria is complicated by ongoing security concerns, which are likely to hamper the polio eradication effort in this area. Nigeria also continues to represent the source of cases exported to neighboring countries.

Chad was one of only two non-endemic countries reporting polio cases in 2012, with 5 cases—all type 1. The last case was reported to have had onset on 14 June 2012. In 2011, Chad had reported 132 cases, representing a precipitous reduction in the Chad polio outbreak. A single instance of type 1 polio occurred in Niger in November. Characterization of the virus suggested importation from Nigeria, but it is thought to have circulated locally, undetected, for some time.

Asia

Pakistan remains the Asian country with the highest number of cases, but also has seen a significant reduction. By the end of 2012, 58 cases were reported, compared to 198 at the same time in 2011. Pakistan is the last remaining locus of type 3 outside Nigeria, having two reported cases, plus one type 1/3 hybrid. Two-thirds of all cases occurred in Balochistan and the Federally Administered Tribal Areas. In the previous year, 198 cases were reported, indicating an improvement in spite of July fatwas from several Pakistani Islamist groups prohibiting vaccination.

Afghanistan also saw a significant reduction in cases, with 37 cases reported by the end of the year, compared to 80 reported in 2011.

End of year totals

The total number of wild-virus cases reported was 223. Of these Nigeria reported 122, Pakistan 58, Afghanistan 37, Chad 5 and Niger 1. Several additional countries, Chad, Democratic Republic of Congo, Somalia and Yemen, saw outbreaks of circulating vaccine-derived polio. In all there were 291 reported polio cases, the smallest number for any year on record.

2013

Reported polio cases in 2013[83]
Country	Wild cases	Circulating vaccine- derived cases	Transmission status
Somalia	194	1	importation
Pakistan	93	48	endemic
Nigeria	53	4	endemic
Syria	35	0	importation
Kenya	14	0	importation
Afghanistan	14	3	endemic
Ethiopia	9	0	importation
Cameroon	4	4	importation
Chad	0	3	cVDPV only
Yemen	0	1	cVDPV only
Niger	0	1	cVDPV only
Total	416	65

A total of 416 wild-virus cases were reported in 2013, compared to 223 cases in 2012. Of these, cases in endemic countries have dropped from 197 to 160 while those in non-endemic countries have risen from 5 to 256. Of the three countries in which polio was endemic, Pakistan, Afghanistan and Nigeria, the latter two have had significantly fewer cases in 2013 than reported in the previous year. An ongoing outbreak centered on Bara in the Federally Administered Tribal Areas of Pakistan, where vaccination has been difficult, represents the major reservoir for the virus in Asia, affecting both Pakistan and neighboring Afghanistan, where there have been no cases in the tradition endemic region in the south. An outbreak in the Horn of Africa, centered in Banadir, Somalia, represented nearly half of the year's total cases, overwhelming the gains made in endemic countries and by September the total number of polio cases has already surpassed that of the entire previous year. There were also cases in Kenya, Ethiopia and Syria. Circulating vaccine-derived cases were also reported in the three endemic countries, as well as Somalia, Chad, Cameroon, Niger and Yemen.^[85] India completed two years without a new polio case, needing one more year before it can be certified polio-free.

WPV3

The sole remaining country in 2012 classified with reestablished transmission, Chad, has passed more than a year since its last wild-virus case, although it is still suffering from an outbreak of vaccine-derived virus. No type 3 cases have been reported in 2013. The last reported type 3 case of polio, world-wide, had its onset 11 November 2012 in Nigeria; the last wild case outside Nigeria was in April 2012 in Pakistan,^[7] and its absence from sewage monitoring in Pakistan suggests that active transmission of this strain has ceased there.^[86]

Asia

An ongoing outbreak centered on Bara in the Federally Administered Tribal Areas of Pakistan represents the major reservoir for the virus in Asia. Vaccination was banned by local leaders in North Waziristan from June, 2012, and the situation has been called alarming. It is also affecting neighboring Afghanistan. Major progress there has resulted in no reported cases in the tradition endemic region in the nation's south. Rather, all cases in Afghanistan in 2013 have been in the northeast and represent spillover from the Pakistani outbreak.

Africa

The year's biggest setback came in the Horn of Africa. Somalia had been free of wild polio since 2007 but had low levels of vaccination that put the nation at risk of reintroduction, and in April a case of polio in Mogadishu was found to be due to a wild polio strain of Nigerian origin.^[87] This came in spite of successful local negotiations the previous year that had allowed access to some populations for the first time in three years and a vigorous vaccination campaign already underway in this area, stricken by an outbreak of circulating vaccine-derived polio ongoing since 2011 that had also spread to neighboring Kenya and Yemen.^[79] The outbreak of wild polio spread to Dadaab, Kenya, home to a large camp hosting Somalian refugees.^[88] Intensive targeted vaccination efforts in both Mogadishu and Dadaab,^[89] as well as more broadly in Ethiopia, Djibouti and Yemen were instituted, but 48 cases caused by wild virus were reported in Somalia and Kenya by early July, and cases have begun to appear in south-central Somalia, where security considerations have compromised vaccination activities for three years. By October, over 170 cases had been reported in Somalia,^[90] with more than a dozen in Kenya and cases in the Somali Region of Ethiopia.

Middle East

Reported polio cases in 2014[83]
Country	Wild cases	Circulating vaccine- derived cases	Transmission status
Pakistan	306	22	endemic
Afghanistan	28	0	endemic
Nigeria	6	30	endemic
Cameroon	5	0	importation
Equatorial Guinea	5	0	importation
Somalia	5	0	importation
Iraq	2	0	importation
Ethiopia	1	0	importation
Syria	1	0	importation
South Sudan	0	2	cVDPV only
Guinea	0	1	cVDPV only
Madagascar	0	1	cVDPV only
Total	359	56

Routine sewage monitoring has revealed the virus in another region that had been polio-free. In late 2012, a PV1 virus strain of Pakistani origin was detected in Cairo, raising fears of reintroduction that sparked a major vaccination push in the city in 2013.^[91] No actual cases of polio were reported there,^[92] but the Cairo strain was later detected in Rahat, Israel in April 2013, and subsequently in Beer Sheba, Kiryat Gat and Ashdod. It has subsequently been detected across the country, indicating a prolonged, widespread transmission. Again, no cases of the disease have been found, and while a large-scale outbreak in Israel is thought unlikely due to their program of routine vaccination and high immunity levels,^[93][94][95] there is thought to be a moderate-to-high risk of further international spread.^[96]

In October and November, World Health Organization confirmed 17 cases of polio in Syria, where immunization rates have dropped significantly because of the civil war. As many as a dozen additional cases await confirmation. It was the first outbreak there in 14 years.^[97] DNA testing revealed the strain to be most closely related to that found in Egypt, and ultimately traces to Pakistan.^[98]

Ongoing programme announcements

In late April, the WHO announced a new $5.5 billion, 6-year cooperative plan (called the 2013–18 Polio Eradication and Endgame Strategic Plan) to eradicate polio from its last reservoirs. The plan calls for mass immunization campaigns in the three remaining endemic countries. It also dictates 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.^[92] In May, Bill Gates announced at the Global Vaccine Summit that total commitments to date stood at $4 billion or 73% of what is needed. This included pledges from Canada ($250 million), Britain ($457 million), Germany ($250 million), Norway ($240 million), Ireland ($6.65 million), Australia ($75.5 million),^[99] the Islamic Development Bank ($227 million) as well as the Gates foundation ($1.8 billion) and other philanthropists ($335 million).^[100]

2014

By the end of 2014, there were 359 reported cases of wild poliomelitis, spread over twelve different countries. Pakistan had the largest number with 328, an increase from 43 in 2013 which is blamed on Al Qaeda and Taliban militants preventing aid workers from vaccinating children in rural regions of the country.^[101] Ethiopia, Guinea, Madagascar and the Syrian Arab Republic each had a single case. The other countries affected were Nigeria (36 cases, down from 49), Afghanistan (28 cases up from 7), Cameroon, Equatorial Guinea, Somalia (5 cases each), Iraq and South Sudan (2 cases each).^[83]

On March 27, 2014, the WHO announced the eradication of poliomyelitis in the South-East Asia Region, in which the WHO includes eleven countries: Bangladesh, Bhutan, North Korea, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste.^[102] With the addition of this region, the proportion of world population living in polio-free regions has reached 80%.^[102] The last case of wild polio in the South-East Asia Region was reported in India on 13 January 2011.^[103]

2015

Reported polio cases in 2015[83]
Country	Wild cases	Circulating vaccine- derived cases	Transmission status	Type(s)
Pakistan	54	2	endemic	WPV1 cVDPV2
Afghanistan	20	0	endemic	WPV1
Madagascar	0	10	cVDPV only	cVDPV1
Laos	0	8	cVDPV only	cVDPV1
Guinea	0	7	cVDPV only	cVDPV2
Ukraine	0	2	cVDPV only	cVDPV1
Myanmar	0	2	cVDPV only	cVDPV2
Nigeria	0	1	cVDPV only	cVDPV2
Total	74	32

74 cases of wild poliomyelitis were reported worldwide during 2015, 53 in Pakistan and 20 in Afghanistan. This represents an 80% reduction of cases compared to 2014, with only 2 countries affected compared to 9.

There were 32 circulating vaccine-derived poliovirus (cVDPV) cases in 2015 compared to 56 cases in the previous year. The most affected countries were Madagascar, Laos, and Guinea while cases in both Pakistan and Nigeria dropped significantly. The WHO decision in 2013 to 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, is taking effect. As ongoing vaccination programs still use some oral vaccine, it is likely there may still be some more cVDPV cases in the future.

On August 17, 2015, the WHO announced that Somalia was free of polio, having not had any reported case of polio for 12 months.^[104] The last case of wild polio virus reported in Nigeria was on 24 July 2014, a major breakthrough in Nigeria's fight against polio,^{[7][105][106]} and on September 25, 2015, the WHO declared that Nigeria was no longer considered endemic for wild polio virus, although type 2 cVDPV is still circulating.^[107]

In early September 2015, there were 2 cases of cVDPV confirmed in the Zakarpattia Oblast of western Ukraine, caused by circulating vaccine-derived type 1 polio virus due to low immunization levels. With the number of children being fully immunized as low as 50%, there was concern a larger outbreak may occur and authorities undertook an emergency outbreak response.^{[108][109][110]} There was also a reported case of vaccine-derived type 2 polio virus in Bamako city, Mali, in a child of Guinean nationality. DNA studies of the virus indicate it originated in Guinea and has been circulating for at least 12 months. Efforts were made to prevent a further outbreak.^[111]

WPV2 was declared eradicated in September 2015 as it has not been seen since 1999 and WPV3 may be eradicated as it has not been seen since 2012. cVDPV type 2 was still causing paralysis in some countries due to a years-long evolution in under-immunized populations.^[63]

2016

Reported polio cases in 2016[83]
Country	Wild cases	Circulating vaccine- derived cases	Transmission status	Type(s)
Pakistan	9	0	endemic	WPV1
Afghanistan	4	0	endemic	WPV1
Laos	0	3	cVDPV only	cVDPV1
Total	13	3

As of 4 May, there have been 13 reported wild polio cases with an onset of paralysis in 2016, down from 23 reported by this time in 2015. Nine have occurred in Pakistan, and four in Afghanistan. There have been three cases of vaccine-derived polio reported so far this year, all of them from Laos in January.

Attacks on polio vaccination campaigns have continued. A suicide bombing in Quetta in January and a pair of attacks by gunmen in Karachi in April targeted Pakistani security personnel protecting vaccinators,^[112][113] while in January three Afghan vaccination workers disappeared and their bodies were found weeks later.^[114]

Because cVDPV2 strains continue to arise from the trivalent oral vaccine that includes attenuated WPV2, between 17 April and 1 May 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 is expected to prevent new strains of cVDPV2 and allow eventual cessation of WPV2 vaccination.^[115]

See also

• Eradication of infectious diseases
• Mathematical modelling of infectious disease
• Population health
• The Final Inch, a documentary film about the eradication effort
• Transmission risks and rates
• List of diseases eliminated from the United States

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External links

• Global Polio Eradication
• Brief Video: Battling Polio on India's Streets Catholic Relief Services