viernes, 18 de mayo de 2012

Progress Toward Interruption of Wild Poliovirus Transmission — Worldwide, January 2011–March 2012

Progress Toward Interruption of Wild Poliovirus Transmission — Worldwide, January 2011–March 2012

Progress Toward Interruption of Wild Poliovirus Transmission — Worldwide, January 2011–March 2012


May 18, 2012 / 61(19);353-357

In January 2012, completion of polio eradication was declared a programmatic emergency for global public health by the Executive Board of the World Health Organization (WHO) (1). Despite major progress since the launch of the Global Polio Eradication Initiative (GPEI) in 1988, circulation of indigenous wild poliovirus (WPV) continues in three countries (Afghanistan, Nigeria, and Pakistan). India has not reported a polio case since January 2011, and is considered polio-free since February 2012. This report highlights progress toward global polio eradication during January 2011–March 2012. The number of polio cases reported globally decreased by 52%, from 1,352 in 2010 to 650 in 2011. Those 650 cases included 341 (53%) reported from the four polio-endemic countries (Afghanistan, India, Nigeria, and Pakistan), 230 (35%) from previously polio-free countries in which WPV importations led to reestablished transmission for ≥12 months (Angola, Chad, and Democratic Republic of the Congo [DRC]), and 79 (12%) from nine countries affected by outbreaks. Compared with 2010, WPV cases increased in 2011 in Afghanistan (69%), Nigeria (66%), and Pakistan (27%), but decreased in India (98%). During January–March 2012, 59% fewer cases were reported worldwide (as of May 15) compared with the same period in 2011, and all cases in 2012 have been reported from Afghanistan, Chad, Nigeria, and Pakistan. Although progress toward polio eradication was substantial in 2011, persistent WPV circulation in 2012, particularly in Nigeria and Pakistan, poses an ongoing threat to eradication efforts, underscoring the need for emergency measures by polio-affected countries and those at risk for outbreaks after importation.
Routine Vaccination Coverage
By the end of 2010, the latest year for which data are available, infant vaccination coverage with 3 doses of trivalent oral poliovirus vaccine (tOPV) by age 12 months was estimated to be 86% globally, 79% in the WHO African Region, 93% in the Region of the Americas, 96% in the European Region and Western Pacific Region, and 77% in the South-East Asia Region (2). However, coverage continues to vary substantially by country and subnationally.
Supplementary Immunization Activities (SIAs)
In 2011, 302 supplementary immunization activities (SIAs)* using oral polio vaccine (OPV) were conducted in 53 countries. The SIAs included 145 national immunization days, 130 subnational immunization days, 17 child health days, and 10 mop-up rounds. Geographically, the SIAs included 57 (19%) SIAs in the four endemic countries, 51 (17%) SIAs in the three countries with reestablished transmission, 61 (20%) SIAs in nine previously polio-free countries affected by outbreaks following importations, and 133 (44%) preventive SIAs in 38 countries with no WPV cases reported during 2011. An estimated 2.35 billion doses of OPV were administered to 430 million persons, primarily children aged <5 years. Of these OPV doses, 41% were tOPV, 5% were monovalent OPV type 1 (OPV1), 1% were monovalent OPV type 3 (OPV3), and 53% were bivalent OPV types 1 and 3 (bOPV). In response to outbreaks with cases in persons aged >5 years, SIAs targeted persons aged ≤39 years in areas of China and the entire population in areas of DRC.
Poliovirus Surveillance
WPV transmission is monitored routinely through surveillance for acute flaccid paralysis (AFP) cases and by stool specimen testing in WHO-accredited laboratories. AFP surveillance performance is monitored using standard indicators for sensitivity (nonpolio AFP rate) and timeliness (stool specimen adequacy)§ (3). All polio-affected countries achieved surveillance performance quality targets during 2011 at the national level, except Côte d'Ivoire. However, the three countries with reestablished transmission and eight of nine countries with WPV outbreaks in 2011 had substantial proportions (>20%) of their populations living in subnational areas with underperforming surveillance systems (3).
Incidence of WPV Cases
Of 650 polio cases reported in 2011, 583 (90%) were WPV1 and 67 (10%) were WPV3, a reduction of 52% and 22%, respectively, compared with 2010. During January–March 2012, 52 cases (43 WPV1, eight WPV3, and one mixed WPV1/WPV3) were reported globally, representing a 63% reduction of WPV1 cases and a 31% reduction of WPV3 cases worldwide compared with the same period in 2011 (Table). In the polio-endemic countries of Afghanistan and Nigeria, more WPV cases were reported in each during January–March 2012 compared with the same period in 2011; in Pakistan, the number of cases decreased during January–March 2012. Since August 2011, WPV3 has been reported only from areas in northern Nigeria and the Federally Administered Tribal Areas of Pakistan.
Countries Considered Polio-Endemic in 2011
Afghanistan. In 2011, 80 cases (all WPV1) were reported, a 69% increase from 25 cases (17 WPV1 and eight WPV3) reported in 2010. As of May 15, 2012, six WPV1 cases were reported during January–March 2012, compared with one WPV1 case reported in the same period of 2011 (Table).
India. One WPV1 case was reported in West Bengal in January 2011, a 98% reduction from 42 WPV1 cases reported in 2010. No WPV cases or WPV isolates from environmental sampling were reported from India during February 2011–March 2012.
Nigeria. In 2011, 62 cases (47 WPV1 and 15 WPV3) were reported, a 66% increase compared with 21 cases (eight WPV1 and 13 WPV3) reported in 2010. During January–March 2012, 28 cases (21 WPV1 and seven WPV3) were reported, compared with eight cases (six WPV1 and two WPV3) reported during the same period of 2011**; foci of WPV transmission in Nigeria include the northwestern states (Sokoto/Zamfara), northcentral states (Kano/Katsina/Jigawa), and northeastern states (Borno/Yobe/Bauchi).
Pakistan. In 2011, 198 cases (196 WPV1 and two WPV3) were reported, a 27% increase from 144 cases (120 WPV1 and 24 WPV3) reported in 2010. During January–March 2012, 15 cases were reported (13 WPV1, one WPV3, and one mixed WPV1/WPV3), compared with 36 WPV1 cases reported during the same period of 2011.†† All WPV3 cases since January 2011 were reported from Khyber Agency, Federally Administrated Tribal Areas. WPV3 was not detected in Khyber from September 2011 to February 2012; the WPV1/WPV3 and WPV3 cases occurred there in March 2012.
Countries with Reestablished Transmission
Angola. In 2011, five WPV1 cases were reported, an 85% reduction from 33 WPV1 cases reported in 2010. The last indication of ongoing circulation of reestablished transmission was a cluster of four WPV1 cases in the southern province of Kuando-Kubango during January–March 2011 (Figure). The most recent WPV1 case, in July 2011, in the northern province of Uige, followed a new importation from DRC (Figure). No cases were reported during January–March 2012, as of May 15, compared with two WPV1 cases reported in the same period in 2011.
Chad. In 2011, 132 cases (129 WPV1 and three WPV3) were reported, an 80% increase from 26 cases (11 WPV1 and 15 WPV3) reported in 2010 (Figure). During January–March 2012, as of May 15, three WPV1 cases were reported, compared with 36 cases (33 WPV1 and three WPV3) reported during the same period of 2011.
DRC. In 2011, 93 cases were reported, compared with 100 in 2010; all were WPV1 (Figure). Two genetically distinct outbreaks occurred in 2011; 79 WPV1 cases reported from January to September in western provinces resulted from importations from Angola and the Republic of the Congo, and 14 WPV1 cases reported from October to December 2011 in the eastern provinces of Katanga and Maniema represented ongoing reestablished transmission originally from importations in 2006 from Angola and continuous circulation in eastern DRC since 2008 or earlier (Figure). No WPV cases were reported during January–March 2012, as of May 15, compared with 42 cases reported in the same period in 2011.
Countries Affected by Outbreaks
In 2011, 11 WPV outbreaks occurred globally, including nine new outbreaks in eight countries and two outbreaks representing transmission from 2010 (WPV3 in Mali and WPV1 in Republic of the Congo) that continued into 2011. The nine new outbreaks in 2011 occurred in western China and in seven countries in Africa (WPV1 in Niger, Central African Republic, Gabon, and Kenya; WPV3 in Côte d'Ivoire, Mali, Niger, and Guinea). In China, 21 WPV1 cases among persons aged ≤53 years (median: 19 years) were reported in the western Xinjiang Uygur Autonomous Region after an importation from Pakistan; this was the first WPV outbreak reported in the WHO Western Pacific Region since 1997. Of the 11 outbreaks, eight were interrupted (i.e., no cases reported in more than 6 months) within 6 months of confirmation and two, in Central African Republic and Niger, are on track to be interrupted within 6 months (no cases have been reported in more than 3 months). The Mali WPV3 2010 outbreak that continued into 2011 was not interrupted within 6 months after confirmation. No new outbreaks have been reported in 2012, to date.

Reported By

Polio Eradication Dept, World Health Organization, Geneva, Switzerland. Global Immunization Div, Center for Global Health; Div of Viral Diseases, National Center for Immunization and Respiratory Diseases; Rennatus M. Mdodo, DrPH, EIS Officer, Div of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention CDC. Corresponding contributor: Steve Wassilak,, 404-639-1867.

Editorial Note

The most significant achievement of the GPEI during January 2011–March 2012 was the interruption of endemic WPV circulation in India, considered polio-free since February 2012. Success in India is attributed to creative approaches by the Indian government and partners, including 1) large-scale mobilization of human and financial resources to increase SIA coverage among children in high-risk endemic areas and migrant populations, 2) introduction of bOPV, 3) improvements in routine vaccination coverage, and 4) rapid responses to new outbreaks (4). India's success proves the technical feasibility of global polio eradication and highlights potential solutions to address operational challenges in other countries. Since 2010, an unprecedented reduction in WPV3 cases also has occurred. Use of bOPV has driven the reduction since 2010. Khyber Agency in Pakistan and several northern states in Nigeria are the only areas where WPV3 cases continue to be reported, a result of low routine vaccination and SIA coverage in limited-access areas (5,6).
Outbreaks following importations into polio-free countries pose a continued threat to the momentum of the GPEI. Large outbreaks occurred in the European Region and in Republic of Congo in 2010 (7); outbreaks in 2011 have been small because of timely detection and prompt response with SIAs. The outbreak in China in 2011 was contained quickly through large-scale SIAs, which in some areas included persons aged ≤39 years. Older age groups have been affected by paralytic polio with high fatality rates in recent outbreaks, and even when not clinically affected, older persons appear to enhance WPV transmission. To reduce the scale and duration of any new outbreaks, GPEI recommends vaccination of all children aged <15 years in the initial response SIAs. Reestablished transmission has continued in some countries because of chronic low population immunity (5). Until WPV transmission in all areas is interrupted, the threat of outbreaks in polio-free areas will continue, requiring all countries to maintain high routine vaccination coverage, sensitive AFP surveillance, and rapid response SIAs to WPV importations. Continued intense WPV transmission in northern Nigeria poses a significant threat for WPV importation and spread into other west and central African countries.
In October 2011, the Independent Monitoring Board of the GPEI stated that the program was not on track for its end of 2012 goal, or for any time soon after, unless fundamental problems were tackled (8). In January 2012, the Executive Board of WHO declared completion of poliovirus eradication a programmatic emergency for global public health (9). In response, each of the remaining countries with endemic or reestablished transmission has developed an emergency action plan for interrupting poliovirus transmission, which includes oversight and accountability mechanisms involving political and health leaders at all administrative levels. National emergency plans specify strategies to vaccinate chronically missed children, improve the quality of SIAs in persistently poor-performing areas, and achieve levels of immunity by end of 2012 that can lead to cessation of transmission. These strategies address inadequate micro-planning,§§ poor selection and performance of vaccination teams, weak supervision, inadequate monitoring, and vaccine refusal. Special strategies were developed to access children in areas of armed conflict. National emergency plans also outline strategies to identify, map, and vaccinate children in migrant and mobile populations and to improve routine immunization services, particularly for high-risk population groups.
Based on national emergency plans and in recognition of global challenges, the GPEI has developed a Global Emergency Action Plan 2012–2013. Key elements include assisting Afghanistan, Nigeria, and Pakistan to significantly increase vaccination coverage by the end of 2012 to levels that will interrupt transmission shortly thereafter; helping to sustain the momentum achieved in Angola, Chad, and DRC to interrupt transmission in 2012; implementing a rigorous accountability process by which health-care workers and administrative leaders will monitor and be held accountable for program performance at the district and state levels; and further improving polio partner accountability and coordination. CDC activated its Emergency Operations Center to better support eradication efforts, in partnership with WHO, Rotary International, the United Nations Children's Fund (UNICEF), the Bill and Melinda Gates Foundation, national ministries of health, and other partner organizations. Funding requirements for the Global Emergency Action Plan 2012–2013 are $2.18 billion. Lack of sufficient funds in the first half of 2012 has forced cancellation and scaling-back of critical SIAs in 24 countries. Full implementation of the national emergency plans is urgently needed or the goal of a polio-free world is at risk.


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  2. World Health Organization. Routine vaccination coverage, 2010.Wkly Epidem Rec 2011;86:509–13.
  3. CDC. Tracking progress toward global polio eradication, 2010–2011. MMWR 2012;61:265–9.
  4. CDC. Progress toward poliomyelitis eradication—India, January 2010–September 2011. MMWR 2011;60:1482–6.
  5. CDC. Progress toward global polio eradication—Africa, 2011. MMWR 2012;61:190–4.
  6. CDC. Progress toward poliomyelitis eradication—Afghanistan and Pakistan, January 2010–September 2011. MMWR 2011;60:1523–7.
  7. CDC. Tracking progress toward global polio eradication, 2009–2010. MMWR 2011;60:441–5.
  8. Independent Monitoring Board of the Global Polio Eradication Initiative. October 2011 report. Geneva, Switzerland: World Health Organization; 2011. Available at Adobe PDF fileExternal Web Site Icon. Accessed April 25, 2012.
  9. World Health Organization Executive Board. Poliomyelitis: intensification of the global eradication initiative. Geneva, Switzerland: World Health Organization; 2012. Available at Adobe PDF fileExternal Web Site Icon. Accessed April 27, 2012.

* Mass campaigns conducted during a short period (days to weeks) nationally or in selected parts of the country (i.e., subnational SIAs), during which a dose of OPV is administered to all children (generally aged <5 years), regardless of previous vaccination history.
Previously polio-free countries with outbreaks include China, Central African Republic, Congo, Cote d'Ivoire, Gabon, Guinea, Kenya, Mali, and Niger.
§ AFP surveillance targets for countries with current or recent WPV transmission include a nonpolio AFP rate of ≥2 cases per 100,000 population aged <15 years, and adequate stool specimen collection from ≥80% of AFP cases.
Most recent WPV3 case reported from a country other than Nigeria or Pakistan had onset of paralysis on August 3, 2011, in Guinea.
** As of May 15, two additional WPV1 cases were reported with onset in April; the most recent case had onset of paralysis on April 7, 2012.
†† As of May 15, an additional WPV3 case was reported with paralysis onset on April 18, 2012.
§§ Detailed pre-campaign planning and mapping at the lowest administrative level, specifying the resource needs and daily expectations for each team.

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