Progress Toward Poliomyelitis Eradication --- Nigeria, January 2004--July 2005

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After the 1988 World Health Assembly resolution to eradicate polio (1), the number of countries where polio is endemic decreased from 125 in 1988 to six* in 2003. However, the Global Polio Eradication Initiative faced critical challenges during 2003--2005, when a resurgence of polio cases occurred across Africa. Nigeria, the most populous^† country of the continent, experienced increased wild poliovirus (WPV) transmission throughout the country after suspension of supplementary immunization activities (SIAs) in certain northern states because of misconceptions regarding vaccine safety (2). The resurgence in Nigeria resulted in the spread of WPV during 2003--2005 into 18 countries that had been polio-free for 1 or more years, including three countries^§ outside Africa (3--6).Transmission was reestablished and is ongoing in six^¶ of these countries. The Nigerian states that suspended campaigns subsequently resumed SIAs in 2004, in synchrony with SIAs being conducted in other countries across West and Central Africa (3). This report summarizes polio eradication activities and WPV circulation in Nigeria during January 2004--July 2005 and the actions under way to interrupt WPV transmission.

Routine Vaccination

In 2003, a national vaccination coverage survey indicated that 31% of children aged <12 months had received 3 doses of diphtheria and tetanus toxoids and pertussis vaccine (DTP3) (range: 6% in the northwest zone** to 68% in the southwest zone); DTP3 is used as a proxy for routine vaccination with 3 doses of oral poliovirus vaccine (OPV3) by age 12 months.

Supplementary Immunization Activities

During 1999--2002, National Immunization Days (NIDs)^†† targeting children aged <5 years were conducted annually (2). In 2003, a global shortfall in international donations restricted SIAs in Nigeria to nine rounds of subnational immunization days (SNIDs)^§§ targeting northern states where polio is endemic. The state governments of Kaduna, Kano, Zamfara, and (to a limited extent) Niger suspended several SIA rounds during 2003--2004. State authorities in Kano, the most populous of these (estimated 2004 population: 7.7 million), suspended all SIAs during April 2003--July 2004 (3), resulting in decreased acceptance of OPV in all the northern states.

Nigeria conducted five NID rounds in 2004, targeting all 37 states (36 states plus the Federal Capital Territory). Kano did not participate in the January and March rounds, and Zamfara missed the January round. With resumption of activities in Kano, SNIDs were conducted in July and September 2004 in eight northwestern Nigerian states^¶¶where polio is endemic. Five NID rounds and one SNID round were planned for 2005; the number of children reached increased steadily with each SIA round during 2004--2005. Independent monitoring indicated a decreasing estimated proportion of households missed nationally (from 7% in October 2004 to 3% in May 2005) and children missed (from 17% to 7%).

Certain populations living in riverine areas (e.g., nomadic cattle herders and fishermen and hard-to-reach settled communities), whose estimated population exceeds 10 million, predominantly in the northern zones, have had limited access to previous SIAs and routine vaccination services. As determined from SIA independent monitoring and polio case investigations, repeatedly missing children in these high-risk populations has contributed substantially to decreased overall childhood population immunity. Specialized teams are now providing outreach activities to reach these groups with OPV and other vaccines. In 2005, to date, approximately 22,000 children from these communities who had never received OPV previously were vaccinated.

The OPV vaccination status (total number of doses through routine and supplementary immunization) of children aged 6--59 months with nonpolio acute flaccid paralysis (NPAFP) is used as a proxy for OPV vaccination of the overall targeted population. In the 13 states where polio is endemic,*** the proportion of NPAFP cases in persons who had received >3 doses of OPV was 15% for cases with onset in the first half of 2004 (range: 1.6%--51%), compared with 19% in the first half of 2005 (range: 0%--60%). In contrast, in the 18 states without confirmed polio in 2005,^††† this proportion was 66% (range: 27%--85%) during the first 6 months of 2004, compared with 71% (range: 40%--96%) during the first 6 months of 2005. During 2004--2005, the proportion of children who had never received OPV declined in only seven of the 13 states where polio is endemic.

AFP Surveillance

Surveillance for AFP is conducted at 4,993 reporting sites in the 774 local government areas (LGAs). AFP surveillance quality is evaluated by using two key performance indicators: 1) annual reporting rate (target: NPAFP incidence rate of >2 cases per 100,000 children aged <15 years^§§§) and 2) completeness of stool specimen collection (target: two adequate specimens from >80% of all persons with AFP^¶¶¶). In 2004, Nigeria achieved a national NPAFP incidence rate of 7.3, when 100% of the 37 states and 65% of the 774 LGAs achieved rates of >2 cases per 100,000 (Table); in 2005, according to provisional data, 68% of LGAs achieved these rates. In 2004, the national collection rate of adequate stool specimens was 91%, when 95% of states and 78% of LGAs attained the target rate of >80%; in 2005, according to provisional data, 56% of LGAs achieved this rate. Surveillance performance at the LGA level varied; in 2004, a total of 296 (38%) LGAs were below the target levels for one or both surveillance indicators; in 2005, a total of 348 (45%) LGAs were below one or both target levels.

WPV Incidence

During 2002--2004, the number of confirmed WPV cases in Nigeria increased from 202 (2002) to 355 (2003) to 782 (2004) (600 WPV type 1 [WPV1], 182 WPV type 3 [WPV3]) (Table, Figure). In 2004, a total of 30 states (81%) and 245 LGAs (32%) reported at least one WPV case, representing a wider area of circulation than in 2002, when 15 states (41%) and 111 LGAs (14%) reported WPV, and in 2003, when 30 states (81%) and 180 LGAs (23%) reported. As of August 26, a total of 377 cases (207 WPV1, 170 WPV3) had been confirmed in 2005 from 19 states (51%) and 135 LGAs (17%), compared with 574 cases (451 WPV1, 123 WPV3) during the same period in 2004.

Of the 782 WPV cases with onset in 2004, a total of 184 (24%) were in Kano (143 WPV1, 41 WPV3), and 532 (68%) were in the other 12 states where polio is endemic (401 WPV1, 131 WPV3). The 2004 WPV1 outbreak peaked in May, whereas outbreaks in previous years peaked in July. The decline in incidence was less steep in the Northwest and Northeast zones, where WPV3 increased in circulation. Of the 782 cases, 717 (92%) occurred in children aged <3 years; 78% of all 782 children were either never or incompletely vaccinated.

In both 2003 and 2004, a total of 32 WPV1 and six WPV3 genetic clusters (of only one genotype each) were observed in circulation.**** In 2005 to date, 14 WPV1 and five WPV3 genetic clusters have been observed in Nigeria, with genetic analyses pending for many isolates.

Reported by: National Programme on Immunization, Federal Ministry of Health; Country Office of the World Health Organization, Abuja; Poliovirus Laboratory, Univ of Ibadan, Ibadan; Poliovirus Laboratory, Univ of Maidugari Teaching Hospital, Maidugari, Nigeria. African Regional Polio Reference Laboratory, National Institute for Communicable Diseases, Johannesburg, South Africa. Vaccine Preventable Diseases, World Health Organization Regional Office for Africa, Harare, Zimbabwe. Immunization, 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.

Editorial Note:

The resurgence of WPV transmission in Nigeria, which began in 2003 and continued into early 2004, was attributable to the suspension of vaccination campaigns in some northern states and the decreasing SIA coverage that preceded suspension because of false rumors about OPV safety (2). However, by July 2004, all states had conducted SIAs. This change was possible because of high-level advocacy by federal authorities, external partners, and public health officials from within the affected states; meetings with religious, traditional, and political leaders; a review by a presidential OPV safety verification committee; and vigorous social mobilization (i.e., public campaigns encouraging persons to accept and seek vaccination). The continued involvement of LGA authorities, together with community traditional and religious leaders, will be essential for continued improvements in SIA implementation and increased routine vaccination levels.

During 2004--2005, the quality of AFP surveillance at state and LGA levels has continued to improve. Remaining gaps at the LGA level are being addressed through training, improved field supervision, ongoing feedback, and peer-performed surveillance assessments.

The resumption of SIAs in July 2004 has resulted in a decreased number of infected states and LGAs as well as an apparent decrease in the genetic diversity of WPVs in 2005. To date, no previously polio-free country has been directly reinfected by Nigeria-derived virus in 2005. Efforts are increasingly being concentrated on the initial 13 polio-endemic states with the most intense transmission of WPVs. Four of the most populous of these (Bauchi, Jigawa, Kano, and Kebbi) have accounted for 258 (68%) of the 377 cases as of August 26, 2005. Data from recent SIAs and OPV history data for NPAFP cases indicate that the program still fails to reach a substantial proportion of children during SIAs in certain areas, particularly in these four states.

Since the beginning of the 2003--2004 outbreak, Nigerian health authorities and immunization partners^†††† have strengthened collaboration through the Interagency Coordination Committee chaired by the Minister of Health, with a leading core group and several working groups. The government of Nigeria and its partner agencies are implementing a strategic plan that focuses on improving the quality of SIAs, particularly within high-risk LGAs and for hard-to-reach populations by enhancing 1) ward-level microplanning (i.e., detailed planning at the lowest administrative level); 2) vaccination team-member selection, training, monitoring, and supervision; 3) provision of logistical support; and 4) social mobilization. In addition, federal, state, and LGA authorities are initiating plans for strengthening routine vaccination service delivery by reestablishing outreach services to improve access to those populations often missed by routine vaccination activities.

The government of Nigeria and its partners are committed to interrupting WPV transmission as soon as possible. Global Polio Eradication Initiative partners are working together at all levels to improve the implementation of strategies to achieve eradication.

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