Poliomyelitis eradication

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

The global eradication of poliomyelitis is a public health effort to eliminate all cases of poliomyelitis (polio) infection around the world. The global effort, begun in 1988 and led by the World Health Organization, UNICEF and The Rotary Foundation, has reduced the number of annual diagnosed cases from the hundreds of thousands to around a thousand. If polio is the next disease to be successfully eradicated, this will represent only the third time this has ever been achieved, after smallpox[1] and rinderpest.[2] The goal of eradicating of worldwide polio has attracted attention, but since 2001 there has been no further reduction in annual cases despite extensive efforts, which has led to getting rid of the last 1% being described as "like trying to squeeze Jell-O to death."[3]

Contents

[edit] Factors influencing eradication

Eradication of polio has been defined in various ways—as elimination of the occurrence of a poliomyelitis even in the absence of human intervention,[4] as extinction of poliovirus, such that the infectious agent no longer exists in nature or in the laboratory,[5] as control of an infection to the point at which transmission of the disease ceased within a specified area,[4] and as reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.[6]

In theory, if the right tools were available, it would be possible to eradicate all infectious diseases which only reside 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.[7] 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.

[edit] 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:[8]

  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[9] among children less than fifteen years of age.
  4. Targeted "mop-up" campaigns once wild poliovirus transmission is limited to a specific focal area.

[edit] Vaccination

Oral polio vaccine is highly effective and inexpensive (about US$0.10 per dose, or US$0.30 per child.[10]) 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.[11] 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.[12][13]

Contact immunity to polio can occur when attenuated poliovirus derived from the oral polio vaccine is excreted, and infects and indirectly vaccinates unvaccinated individuals.[14]

[edit] Herd immunity

Polio vaccination is also important in the development of herd immunity.[15] 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.[14] 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 if the number of susceptible individuals can be reduced to a small number through vaccination, the pathogen itself can also be eliminated.

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 between 0–8° Celsius (32–46° Fahrenheit)) without a human host the virus dies out.[16]

Herd immunity is an important supplement to vaccination. Among those individuals who receive oral polio vaccine, only 95 percent will develop immunity.[17] That means 5 of every 100 given the vaccine won’t 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.[15] 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.[15] If routine immunization were stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.[18]

[edit] 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 vertical (top down) intervention. 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 2-8°Celsius for vaccination to be successful.[12]

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 district and Uttar Pradesh, 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.[19]

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 [20] and most infected people are unaware that they carry the disease, allowing polio to spread widely before cases are seen.[21] 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.[22]

[edit] Progress

International Polio Cases and Countries reporting Cases by Year
Year Estimated Recorded Countries
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 - 2,971[23]
2001 - 483 15
2002 - 1,918 9
2003 - 784 15
2004 - 1,258 18
2005 - 1,979 16
2006 - 1,997 17
2007 - 1,315 12
2008 - 1,651 18
2009 - 1,604 23
2010 - 1,294 20
References:[12][24][25][26][27]

Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries.[17] Czechoslovakia became the first country in the world to scientifically demonstrate nationwide eradication of poliomyelitis in 1960.[28] 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.[29] The Pan American Health Organization (PAHO), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the Americas in 1985.[30]

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.[31]

[edit] 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.[30] The last case of wild poliovirus poliomyelitis in the Americas was reported in Peru, August 1991.[30]

[edit] 1994–2000

On 20 August 1994 the Americas were certified as polio-free.[32] 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.[33]

In 1995 Operation MECACAR (Mediterranean, Caucasus, Central Asian Republics and Russia) were launched; National Immunization Days were coordinated in 19 European and Mediterranean countries.[34] In 1998, Melik Minas of Turkey became the last case of polio reported in Europe.[35] In 1997 Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region.[36] In 2000 the Western Pacific Region (including China) was certified Polio-free.[36]

In October 1999, the last isolation of type 2 poliovirus occurred in India. This type of poliovirus appears to have been eradicated.[17]

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.[37]

[edit] 2001–2004

By 2001, 575 million children (almost one-tenth the world's population) had received some 2 billion doses of oral polio vaccine.[24] The World Health Organization announced that Europe was polio-free on June 21, 2002 in the Copenhagen Glyptotek.[38]

In 2002, an outbreak of polio in India occurred. 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.[39] (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 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.[30] 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 Ivory Coast have complicated WHO's polio eradication goal. In 2004, almost two-thirds all the polio cases in the world occurred in Nigeria (760 out of 1170 total).

[edit] 2005

Reported Polio Cases in 2005
Polio worldwide 2005.svg
Country Cases Transmission
Status
Nigeria 830 endemic
Yemen 478 importation
Indonesia 303 importation
Somalia 185 importation
India 66 endemic
Pakistan 27 endemic
Sudan 27 re-established
transmission
Ethiopia 22 importation
Angola 10 importation
Niger 10 importation
Afghanistan 9 endemic
Nepal 4 importation
Mali 3 importation
Chad, Eritrea,
Cameroon		 1 ea. importation

There were 1,979 cases of wild poliovirus (excludes vaccine derived polio viruses) in 2005.[25] 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.[26]

Yemen, Indonesia and Sudan, countries which had been declared polio-free since before 2000, each reported hundreds of cases - probably imported from Nigeria.[40] 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.[41]

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).[42]

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 vaccinations were 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 unvaccinated for polio.[43]

[edit] 2006–2009

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.[25] 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.[44] (See: Map of reported polio cases in 2006)

In 2007 there were 1,315 cases of poliomyelitis reported worldwide.[25] 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.[40] 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.[45]

One factor in the failure of polio immunization programs has been opposition by Muslim fundamentalists. This opposition has varied and is linked mostly to local political will rather than any religious orthodoxy. In Pakistan and Afghanistan, the Taliban have issued fatwas against polio vaccination, while Saudi Arabia has supported the eradication effort by demanding that all pilgrims to the Haj that originate from polio endemic countries receive vaccination upon arrival. But even with the express support of political leaders, polio workers have been kidnapped, beaten, and assassinated.[46] 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.[47] In July 2007, a student traveling from Pakistan imported the first polio case to Australia in over 20 years.[48] 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.[25]

In 2008, 19 countries reported cases and the total number of cases was 1652. Of these, 1506 occurred in the four endemic countries (146 elsewhere). The largest number were in Nigeria (799 cases) and India (559 cases): these two countries contributed 82.2% of all cases. Outside endemic countries Chad reported the greatest number (37 cases).[25]

In 2009, a total of 1606 cases were reported in 23 countries. 1256 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).[25] 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.

[edit] 2010

According to figures updated in June 2011, the World Health Organization reports that there were 1,349 cases of wild polio in 20 countries in 2010. Reported cases of polio are 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). 457 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 have so far been 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).[25][49]

[edit] 2011

Up to the end of April 33 cases were reported in Pakistan, eight in Nigeria and only one in both India and Afghanistan.

To the end of June 2011 241 cases globally have been reported (216 wild poliovirus type 1 and 25 wild polio type 3). This compares with 456 cases reported to the end of May in 2010 (399 type 1 and 57 type 3). Cases have been reported in the four endemic countries -- Pakistan, Afghanistan, Nigeria and India -- as well as in the Democratic Republic of Congo, Chad, Angola, Mali, Cote d'Ivoire, Burkina Faso, the Republic of Congo (Brazzaville), Niger and Gabon. Over 80% of all cases seen this year come from three countries: Chad, the Democratic Republic of the Congo and Pakistan. In India, only 1 case of wild poliovirus has been reported this year--a remarkable feat in a country that in many recent years has had a plurality or majority of the world's polio cases.[50]

Since the start of 2010 there have been 14 outbreaks of polio. Several are continuing into 2011. To June 2011 Chad has reported 80 cases; the Democratic Republic of the Congo has reported 59; and Pakistan has reported 54. Polio transmission has recurred in Angola, Chad and the Democratic Republic of the Congo. The number of cases reported in Pakistan is double the number reported over the same period in 2010. 16 cases have been reported in Nigeria. Although the situation in Northern Nigeria has improved, concerns exist about further outbreaks there because of its central location. On the basis of current trends it would appear that Pakistan will be the be last place of Earth where wild polio will survive.

Up to the end of August there have been 364 cases reported (308 type 1 and 56 type 3). Up to the same date in 2010 there were 641 cases (574 type 1 and 67 type 3). Kenya has reported its first case since 2009. China has reported four cases - the first cases since 1994. Côte d'Ivoire has reported 34 cases of type 3 polio as part of an ongoing outbreak. Afghanistan has reported 18 cases (all type 1). Chad has reported 109 cases. India has reported no case since January.

The situation in Pakistan is complex. The lowest number of cases reported in one year was 32 in 2007. In the first six months of 2011 there were 69 cases (compared with 37 in the same period in 2010). The remaining focuses lie in three parts of Pakistan: Balochistan Province, Karachi and the Federally Administered Tribal Areas.[51] 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[52].

Up to the end of September there have been 429 cases - 370 due to type 1 and 59 due to type 3. 36 have been reported in Afghanistan. Chad has reported 111 cases. 10 have been reported in China: all have occurred in the Xinjiang Uygur - 9 in Hotan prefecture

[edit] See also

[edit] References

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  52. ^ CIA organised fake vaccination drive to get Osama bin Laden's family DNA http://www.guardian.co.uk/world/2011/jul/11/cia-fake-vaccinations-osama-bin-ladens-dna

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