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Progress Toward Poliomyelitis Eradication --- Nigeria, January 2002--March 2003
Since 1988, when the World Health Assembly resolved to eradicate poliomyelitis globally, the annual estimated incidence of polio has decreased >99% (1,2). Nigeria is the most populous country in Africa (estimated 2000 population: 127 million) and a major poliovirus reservoir. This report summarizes progress toward polio eradication in Nigeria during January 2002--March 2003, highlighting progress in acute flaccid paralysis (AFP) surveillance and evidence of wild poliovirus (WPV) circulation in areas of lower vaccination coverage. The findings underscore the importance of achieving high-quality supplementary immunization activities (SIAs).
National routine vaccination services remain inadequate. In 2000, an estimated 38% of infants aged <1 year received 3 doses of oral polio vaccine (OPV) (3), and in 2001, an estimated 25% of infants aged <1 year received 3 doses of OPV (World Health Organization [WHO] and United Nations Children's Fund [UNICEF], unpublished data, 2003).
Supplementary Immunization Activities
Supplementary OPV vaccination activities targeting children aged <59 months have been conducted annually in Nigeria since National Immunization Days (NIDs)* were begun in 1996 (4). During 2002--2003, the frequency of SIA rounds in Nigeria has been sustained. In 2002, three rounds of NIDs, two rounds of Subnational Immunization Days (SNIDs), and additional mop-up rounds were conducted. As of May 2003, five rounds of SNIDs and additional mop-up rounds had been completed; one SNID covering eight states in which polio is endemic and two NIDs are scheduled for October and November. NIDs were conducted in October and November 2002, reaching approximately 36.0 and 38.9 million children aged <5 years, respectively. SNIDs in high-risk areas were conducted in April and May 2002 and in January, March, and April 2003. The first series of SNIDs targeted eight northcentral and northeastern states in January and March, reaching approximately 12.5 million children aged <5 years, and six states in April, reaching approximately 5.2 million children aged <5 years. In March and April, a second series of SNID rounds was conducted in four northwestern states, reaching approximately 3.8 and 3.7 million children aged <5 years, respectively. In February and March 2003, two mop-up rounds were conducted in response to an outbreak in Nasarawa, a state in which no WPV had been isolated for >12 months. In May and June 2003, additional mop-up activities were implemented in 16 local government areas (LGAs) in Benue, Kogi, and Nasarawa states. During 2001--2002, the number of national and international staff trained and deployed to plan, implement, and monitor SIAs increased threefold, and independent monitoring of SIA quality indicators and of social mobilization activities also was intensified and expanded.
National polio eradication programs analyze the OPV vaccination status (routine and supplemental doses) of children aged <5 years with nonpolio AFP as a proxy for OPV coverage in the general population. During March 2002--February 2003, the proportion of children aged <5 years with nonpolio AFP who received >3 doses of OPV was <60% (median: 44%; range: 37%--59%) in 12 of the 20 northern states and >80% in two states. By contrast, during the same period, the proportion of children aged <5 years with nonpolio AFP who received >3 doses of OPV was >80% (median: 86%; range: 83%--95%) in seven of the 17 southern states and <60% in one state. Although >90% of children targeted were reached with OPV during the 2002 NIDs and three of the five rounds of SNIDs conducted as of March 2003, some LGAs have failed to reach >80% of target children. During the January and March 2003 SNIDs conducted in eight northern states (Bauchi, Borno, Gombe, Jigawa, Kaduna, Kano, Katsina, and Yobe), the number of LGAs reporting coverage of <80% increased from 43 (21%) of 203 in January to 72 (35%) of 203 in March. Coverage in these LGAs was low because vaccinators missed some houses and persons in these areas were poorly informed about SIAs.
Surveillance for AFP
AFP surveillance quality is evaluated by two key indicators: annual reporting rate (target: nonpolio AFP rate of >1 case per 100,000 children aged <15 years) and completeness of specimen collection (target: two adequate stool specimens from >80% of all persons with AFP). In 2002, the nonpolio AFP rate was >1.0 in all 36 states and the Federal Capital Territory of Abuja. During 2001--2002, the nonpolio AFP rate increased from 3.8 to 5.7, and the adequate stool specimen collection rate increased from 68% to 84% (Table). In 2002, in 35 (95%) of 37 states, collection of two adequate stool specimens was >80%. During January--March 2003, the annualized nonpolio AFP rate was 4.2; two adequate stool specimens were collected for 91% of persons with AFP, and 33 (89%) of 37 states had adequate stool specimen collection rates of >80%.
The AFP surveillance system is supported by two national WHO-accredited laboratories, one each in Ibadan (Oyo state) and Maiduguri (Borno state). During 2001--2002, the number of stool specimens processed by these laboratories increased from 3,935 to 6,164. The rate of isolating nonpolio enteroviruses (NPEVs) is a combined indicator of the quality of stool specimen transport and sensitivity of laboratory processing. In 2002, the NPEV isolation rate was 15% at the Ibadan and 18% at the Maiduguri laboratory (anticipated minimum: >10%). During January--March 2003, NPEV isolation rates at both laboratories were 13% and 8%, respectively.
Wild Poliovirus Incidence
During 2001--2002, improvements in AFP surveillance were associated with an increase in the number of WPV cases detected, from 56 in 2001 to 202 in 2002 (Table). As of March 31, 2003, a total of 32 WPV cases had been detected. Since July 2001, no WPVs have been isolated in 17 southern states (Abia, Akwa Ibom, Anambra, Bayelsa, Cross River, Delta, Ebonyi, Edo, Ekiti, Enugu, Imo, Lagos, Ogun, Ondo, Osun, Oyo, and Rivers), or from four central states (Adamawa, Kwara, Plateau, and Taraba). Genetic analysis of WPV isolates has demonstrated the disappearance of lineages, suggesting that many chains of transmission have been broken. However, intense WPV transmission continued in the northern states during 2002--2003 (Figure). During 2002, five northern states (Bauchi, Jigawa, Kaduna, Kano, and Katsina) accounted for 133 (66%) of 202 WPV isolates. Kano state alone accounted for 51 (25%) of 202 WPVs detected during 2002 and for 16 (50%) of 32 WPVs detected during January--March 2003. In previous years in Nigeria, transmission peaked during September--November, but during 2002, a broader peak in transmission occurred during April--November, encompassing 178 (88%) of 202 cases; of 202 confirmed cases detected in 2002, a total of 95 (47%) were among children aged <2 years; of 167 patients for whom vaccination status was reported, 33 (20%) had never received OPV.
Reported by: Federal Ministry of Health; Country Office of the World Health Organization, Abuja, Nigeria. Vaccine Preventable Diseases, World Health Organization Regional Office for Africa, Harare, Zimbabwe. Vaccines and Biologicals Dept, World Health Organization, Geneva, Switzerland. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Global Immunization Div, National Immunization Program, CDC.
During 2002--2003, AFP surveillance improved substantially in Nigeria. The genetic sequencing data from polioviruses isolated indicate that several genetic lineages have been eliminated. Demonstration of the absence of wild virus circulation in 14 southern states since 2001 is encouraging and provides evidence that implementation of similar high-quality eradication activities can interrupt transmission in the northern states. Other achievements during 2001--2002 include increased frequency and improved implementation of SIA monitoring and regular analysis of SIA quality indicators.
Despite progress, Nigeria remains one of three global poliovirus reservoirs (along with northern India and Pakistan) whose low routine OPV vaccination coverage and high population density favor poliovirus transmission. Several factors raise concern about the quality of SIA implementation. During January--March 2003, despite sustained implementation of SIAs targeting high-risk states, the number of areas in which OPV coverage was <80% increased. During 2002, the number of persons with confirmed WPV increased approximately fourfold, and 20% of these persons had never received OPV. The detection of substantial numbers of confirmed cases outside the peak transmission season in 2002 and the isolation of WPV type 3 from 22 patients during January--March 2003 (i.e., during the seasonal low point of transmission) suggest a persistent gap in population immunity in northern states. Improved SIA monitoring has attributed low vaccination coverage to houses being missed by vaccinators and pockets of poorly informed parents. These findings indicate a need for higher quality vaccination activities overall, including better planning, more coordinated social mobilization and communication activities, and continued intensive monitoring. For SIAs to be improved, the high degree of political commitment that exists at the national level should be translated into greater involvement and accountability at the state and LGA levels.
In addition to SIA activities, the government of Nigeria is working with partners to strengthen routine vaccination. In 2002, with the support of WHO and UNICEF, the country developed a 5-year cold chain rehabilitation plan. With a grant from the Global Alliance for Vaccines and Immunization vaccine fund in 2002, the Ministry of Health (MOH) is developing new interventions, including training of health-care workers in charge of vaccination services at state and local government areas and a review of the vaccine distribution system. MOH also has received technical support from newly recruited national consultants to assist in planning, implementation, and monitoring of the vaccination services at the state level.
Upcoming planned activities include SNIDs in September 2003 in the northern states (the extent to be determined at a meeting of an expert advisory group in July) and NIDs in October and November 2003. Close collaboration between the government and its global partners has been critical in sustaining eradication activities in Nigeria and will continue to be essential to achieve polio eradication§.
* Mass campaigns during a short period (days) in which 2 doses of OPV are administered to all children in the target group (usually those aged <5 years) regardless of previous vaccination history.
Campaigns similar to NIDs but confined to part of the country.
§ Polio eradication efforts in Nigeria are supported by the governments of Nigeria, Japan, the Netherlands, and Norway; the European Union; the International Development Agency, Canada; the Department for International Development, United Kingdom; the U.S. Agency for International Development and Basic Support for Institutionalizing Child Survival (BASICS); Rotary International; UNICEF; WHO; and CDC.
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