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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), the United Nations Children's Fund (UNICEF) and the Rotary Foundation, has reduced the number of annual diagnosed wild polio cases from the hundreds of thousands to 22 in 2017.
Of the three strains of polio virus, the last recorded wild case caused by type 2 (WPV2) was in 1999. Type 3 (WPV3) is last known to have caused polio on 11 November 2012, with all wild-virus cases since that date being due to type 1 (WPV1). Mutated vaccine strains can also result in polio, and so-called circulating vaccine-derived cases of type 1 (cVDPV1) and 2 (cVDPV2) continue to be detected. If polio is the next disease to be successfully eradicated, this will represent only the third time this has ever been achieved, after smallpox and rinderpest.
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 ten 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". Since 2011 incidence rates of the disease have dropped dramatically, and with large reductions continuing through to 2017, hopes for eliminating polio have been rekindled.
India is the latest country to have officially stopped endemic transmission of polio—with its last reported case in 2011. Only three countries remain where the disease is endemic—Afghanistan, Pakistan and Nigeria.
Factors influencing eradication of polioEdit
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 of poliovirus, 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 of the disease ceased within a specified area, and 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; 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.
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:
- 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.
- Organization of "national immunization days" to provide supplementary doses of oral polio vaccine to all children less than five years old.
- 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. among children less than fifteen years old.
- Targeted "mop-up" campaigns once wild poliovirus transmission is limited to a specific focal area.
Oral polio vaccine is highly effective and inexpensive (about US$0.10 per dose, or US$0.30 per child) 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. 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.
Polio vaccination is also important in the development of herd immunity. 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. 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.
Herd immunity is an important supplement to vaccination. Among those individuals who receive oral polio vaccine, only 95 percent will develop immunity. 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. 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. If routine immunization were stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.
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.
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.
Two additional challenges are found in unobserved polio transmission and in vaccine-derived poliovirus. First, most polio infections are asymptomatic or result in minor symptoms, with less 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. 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. 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.
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."
Opposition and aid worker killingsEdit
One factor contributing to the continued circulation of polio immunization programs has been opposition in some countries. In Pakistan and Afghanistan, the Taliban have issued fatwas against polio vaccination.
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. 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. 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. Pakistan reported the world's highest number of polio cases (198) in 2011. 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".
Even with the express support of political leaders, polio workers have been kidnapped, beaten, and assassinated. 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. In 2012, there was the killing of a polio worker in Gadap in October. In December 2012, a three-day vaccination campaign sponsored by the United Nations agencies the World Health Organization and UNICEF in Pakistan was suspended following the murder of nine vaccination workers.
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, but amid worries that this would inspire hostility, some escorts have been refused. Both escorting officers and polio workers continue to be killed in Pakistan, where vaccination has been said to violate Islamic law. In February a pair of similar attacks in Nigeria killed nine female polio vaccinators following a local cleric's condemnation of vaccination. 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. In December 2013, three polio workers were killed in northwest Pakistan and three more were killed in Karachi in January 2014.
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, which 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.
Polio eradication criteriaEdit
A country is regarded as polio free or non-endemic if no cases have been detected for a year. However, it is still possible polio circulates 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 the currently circulating virus WPV1, only 1 in 200 infection cases exhibit symptoms of polio paralysis in non-vaccinated children, and possibly even fewer in vaccinated children. Therefore, even a single case is considered an epidemic. According to modeling, it can take four to six months of no reported cases to achieve only a 50% chance of eradication, and one to two years for e.g. 95% chance. Sensitivity of monitoring for circulation can be improved by sampling sewage. In Pakistan in the last couple of years, the number of paralysis cases has dropped relatively faster than the positive environmental samples. The presence of multiple infections with the same strain in the upstream area may not be detectable, so there are some saturation effects when monitoring the number of positive environmental samples.  Furthermore, virus may shed beyond the expected duration of several weeks in certain individuals. Contagiousness can not be readily excluded. For a polio virus to be certified as eradicated worldwide, at least three years of good surveillance without cases needs to be achieved, though this period may need to be longer for a strain like WPV3, where a lower proportion of those infected demonstrate symptoms, or if sewer samples stay positive. Wild poliovirus type 2 was certified eradicated in 2015, the last case having been detected in 1999. Wild poliovirus type 3 has not been detected since 2012, but its eradication has yet to be certified, and the Global Commission for the Certification of Poliomyelitis Eradication in 2017 recommended not certifying its eradication independent of that of WPV1, and hence of wild poliovirus as a whole. This recommendation would mean that type WPV3 will not be removed from the bivalent oral vaccine, as was considered necessary with WPV2 due to its high risk of giving rise to cVDPV strains, but rather oral vaccination for WPV3 will continue until total eradication of polio allows all oral vaccination to cease.
Progress and setbacksEdit
|International wild poliovirus cases by year|
Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. Czechoslovakia 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 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), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the Americas in 1985.
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. The last case of wild poliovirus poliomyelitis in the Americas was reported in Peru, 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 1995 Operation MECACAR (Mediterranean, Caucasus, Central Asian Republics and Russia) were launched; National Immunization Days were coordinated in 19 European and Mediterranean countries. In 1998, Melik Minas of Turkey became the last case of polio reported in Europe. In 1997 Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region. In 2000 the Western Pacific Region (including China) was certified polio-free.
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.
By 2001, 575 million children (almost one-tenth the world's population) had received some 2 billion doses of oral polio vaccine. The World Health Organization announced that Europe was polio-free on 21 June 2002, in the Copenhagen Glyptotek.
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. (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. 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 $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).
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, 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 (excludes vaccine-derived polio viruses). Most cases were located in two areas: the Indian subcontinent and Nigeria. Eradication efforts in the Indian sub-continent 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.
Yemen, Indonesia and Sudan, 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, 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.
In the United States on 29 September 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.
In 2006 only four countries in the world (Nigeria, India, Pakistan and Afghanistan) 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 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. (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; 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. 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.
In July 2007, a student traveling from Pakistan imported the first polio case to Australia in over 20 years. 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.
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).
In 2009, a total of 1,606 cases were reported in 23 countries. Four endemic countries accounted for 1,256 of these, 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). 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 WHO reported 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). An acute outbreak in Tajikistan gave rise to 460 cases (34% of the global total), and 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 25 September. These were the first cases in the WHO European region since 2002. The Republic of Congo (Brazzaville) 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 type 1 outbreak in Angola (33 cases in 2010) and the Democratic Republic of the Congo (100 cases).
In 2011, 650 WPV cases were reported in 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 reported its first case since 2009, while China reported 21 cases, mostly among the Uyghurs of Hotan prefecture, Xinjiang, the first 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, Democratic Republic of the Congo, Somalia and Yemen, saw outbreaks of circulating vaccine-derived polio. The last reported type 3 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 owing to two outbreaks: one in the Horn of Africa, and one in Syria.
In April, a case of wild polio in Mogadishu 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 of Ethiopia.
Routine sewage monitoring in 2012 had detected a WPV1 strain of Pakistani origin in Cairo, 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 late April 2013, 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 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 is 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, Bhutan, North Korea, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste. 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. In comparison, there were 359 cases in 2014. There were 32 circulating vaccine-derived poliovirus (cVDPV) cases in 2015 compared to 56 cases in the previous year.
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. WPV1 resurfaced in Nigeria the following year.
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.
Reported polio cases in 2011
|Central African Republic||4||0||importation|
|Republic of the Congo||1||0||importation|
Reported polio cases in 2012
Reported polio cases in 2013
Reported polio cases in 2014
|South Sudan||0||2||cVDPV only|
Reported polio cases in 2015
Reported polio cases in 2016
There were 37 reported WPV1 cases with an onset of paralysis in 2016, half as many as in 2015. Twenty of these cases occurred in Pakistan, thirteen in Afghanistan, and four in Nigeria. The cases of WPV1 in Nigeria were viewed as a setback, there having been no detected cases caused by the wild virus there in almost two years, yet genetic analysis showed that the virus was of a strain circulating undetected since 2011 in regions inaccessible due to the activities of Boko Haram.
The 2015 cVDPV1 outbreak in Laos continued into 2016, with three cases in January. Two separate strains of cVDPV2 were reported in Nigeria's Borno and Sekoto states, the latter resulting in one case. In Pakistan a new strain of cVDPV2 arose in the Quetta area, with one instance of paralysis.
Environmental samples from Hyderabad, India from January 2015 to May 2016 showed the ongoing presence of a cVDPV2 strain in that city, without diagnosed cases. Due to shortages in the global supply of injectable vaccine, an emergency campaign was launched using vaccine at one fifth the normal dose (fractional-Dose Inactivated Polio Vaccine, or fIPV), the first mass vaccination using this dosage of injectable vaccine.
Attacks on polio vaccination campaigns 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, while in January three Afghan vaccination workers disappeared and their bodies were found weeks later.
Because cVDPV2 strains continued to arise from trivalent oral vaccine that included attenuated WPV2, in April and 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 from arising and allow eventual cessation of WPV2 vaccination.
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 remains 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 resulted in one asymptomatic infection.
Laos was declared free of cVDPV1 in March, but two distinct cVDPV2 outbreaks occurred in the Democratic Republic of the Congo. One in Maniema province resulted in two April polio cases, and a second in February in Haut-Lomami and neighboring Tanganyika provinces came from a virus circulating there for at least a year, and had caused 20 cases by year's end and continued into the next year. In Syria a large outbreak began at Mayadin, Deir ez-Zor Governorate, a center of fighting in the Syrian Civil Warand 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.
The 2016 global switch in vaccination methods resulted in shortages of the injectable vaccine, and led the WHO in April 2017 to recommend general use of the fIPV vaccination protocol, involving subcutaneous injection of a lower dose than used in the standard intramuscular delivery.
Reported polio cases in 2018
The outbreak of cVDPV in the Democratic Republic of Congo continued, with three January cases reported in Tanganyika and Haut-Lomami provinces. In Banaadir, Somalia, and Nairobi, Kenya, environmental samples have tested positive for the cVDPV2 strain first detected in Somalia the previous year, though no cases of paralysis have been attributed to it in either country.
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