Progress Toward Poliomyelitis Eradication — Nigeria, January 2011–September 2012

In 1988, the World Health Assembly launched the Global Polio Eradication Initiative (GPEI) and, in 2012, declared the completion of polio eradication a programmatic emergency for global public health (1). To date, wild poliovirus (WPV) cases reported worldwide in 2012 are at historically low levels. Nigeria is one of only three countries with uninterrupted WPV transmission (in addition to Pakistan and Afghanistan) and has been the origin of WPV imported into 25 previously polio-free countries since 2003 (2–4). This report updates previous reports (2–3,5) and describes polio eradication activities and progress in Nigeria during January 2011–September 2012, as of October 30, 2012. The number of reported WPV cases increased from 21 in 2010 to 62 in 2011. During January–September 2012, a total of 99 WPV cases were reported, more than doubling from the 42 cases reported during the same period in 2011. During 2011, a total of 32 circulating vaccine-derived polio virus type 2 (cVDPV2) cases were confirmed; six cVDPV2 cases were confirmed during January–September 2012, compared with 18 cVDPV2 cases during the same period in 2011. Nigeria's 2012 Polio Eradication Emergency Plan (6) includes senior government leadership oversight, new program management and strategic initiatives, an accountability framework, and a surge in human resources to address chronically missed children during supplemental immunization activities (SIAs).* In 2012, indicators of immunization campaign quality show modest improvements; available data indicate gaps in surveillance. Continuing WPV transmission in Nigeria poses an ongoing risk for WPV reintroduction and outbreaks in polio-free countries and is a major obstacle to achieving global eradication (7).

Vaccination Activities

Infants and children are vaccinated against polio as part of a routine vaccination program and through SIAs. The estimated national routine vaccination coverage of infants with 3 doses of trivalent oral poliovirus vaccine (OPV) in Nigeria was 73% in 2011, compared with 54% in 2007 (8). Surveys indicate substantially lower coverage than the national average in the northern states, with wide variation within the majority of northern states.†

During January 2011–September 2012, one national and 10 subnational SIAs were conducted, primarily in high-risk northern states, targeting children aged <5 years using bivalent OPV type 1 and 3, as well as three national and four subnational SIAs using trivalent OPV. After the four campaigns conducted during January–September 2012, lot quality-assurance sampling§ surveys were used to assess the quality of SIAs in reaching all children. The proportion of sampled local government areas (LGAs) (equivalent to districts), in the 12 high-risk northern states that failed to meet the <20% missed children threshold was 82% (72 of 88) after the February 2012 SIA; the proportion decreased over subsequent SIAs: 74% (68 of 92) after the March SIA, 65% (70 of 108) after the May SIA, and 63% (91 of 145) after the July SIA.¶

A surrogate measure of OPV coverage through routine vaccination and SIAs is based on parental recall and vaccination cards of children aged 6–35 months with acute flaccid paralysis (AFP) not attributed to poliovirus (nonpolio AFP [NPAFP]). During all of 2011 and January–September 2012, 3% of children aged 6–35 months in high-risk northern states with NPAFP had never received a dose of OPV ("zero-dose children"), compared with 7% in 2010; the proportion of children in high-risk northern states with NPAFP cases who received ≥4 doses of OPV was 75% in 2011 and 76% during January–September 2012, compared with 60% in 2010 (Table).

Poliovirus Surveillance

AFP surveillance. Polio surveillance depends on detection of AFP cases with confirmation of poliomyelitis by viral isolation. Quality surveillance is measured through performance indicators with defined targets: NPAFP detection rates of ≥2 cases per 100,000 children aged <15 years and adequate stool specimen collection** in ≥80% of AFP cases. In 2011, the annual national NPAFP rate (per 100,000 population aged <15 years) was 7.9, and the proportion of AFP cases with adequate specimen collection was 93%. To date, the annualized national NPAFP rate in 2012 is 9.2, and the proportion of AFP cases with adequate specimen collection is 94%. Both indicators were met in all states during 2011 and all but one state during January–September 2012 (Table). The proportions of LGAs in high-risk northern states that met each indicator in 2011 and January–September 2012 were 82% and 80%, respectively.

Environmental surveillance. To supplement AFP surveillance, collection of sewage samples every 4–5 weeks for poliovirus testing began in July 2011 at three sites in Kano state. During July–December 2011, cVDPV2 was isolated from 12 (67%) of 18 samples collected from Kano; during January–September 2012, of 25 collected, WPV type 3 (WPV3) was isolated from one specimen (4%), and cVDPV2 was isolated from three specimens (12%). Environmental surveillance every 2 weeks at four sites in Sokoto began in March 2012, and WPV1 and cVDPV2 were detected in 15 specimens (30%) and 22 specimens (44%), respectively, of 50 collected. During January–September 2012, AFP surveillance confirmed 18 WPV1, three WPV3, and three cVDPV2 cases in Kano; in Sokoto, eight WPV1 cases and three cVDPV2 cases were confirmed, indicating variability in environmental surveillance sensitivity possibly attributable to site selection.

WPV and cVDPV Case Incidence

During 2011, a total of 62 WPV (47 WPV1 and 15 WPV3) cases were reported in Nigeria, compared with 21 (eight WPV1 and 13 WPV3) cases in 2010, an increase of 195%; 99 WPV (82 WPV1 and 17 WPV3) cases were reported during January–September 2012, compared with 42 (33 WPV1 and nine WPV3) cases during the same period in 2011 (Figures 1 and 2), an increase of 136%. Cases occurred in 42 LGAs in eight states in 2011 and 55 LGAs in 11 states in 2012; all cases occurred in high-risk northern states, with the exception of one WPV3 case reported in Taraba in July 2012. Of 161 cases with onset during January 2011–September 2012, 148 (92%) occurred in children aged <5 years, and 13 (8%) occurred among children aged 5–14 years; 40 (25%) were "zero-dose" children, and 58 (36%) were children reported to have received ≥4 doses of OPV.

During 2011, a total of 32 cVDPV2 transmission cases were confirmed, a 19% increase from 27 cVDPV2 cases in 2010; six cVDPV2 cases were reported during January–September 2012, a 67% decrease from 18 cases during the same period in 2011 (Figures 1 and 2). Cases occurred in 27 LGAs in eight states in 2011 and three LGAs in two states (Kano and Sokoto) in 2012. Of 38 cases with onset during January 2011–September 2012, a total of 37 (97%) occurred in children aged <5 years, and one (3%) occurred among children aged 5–14 years; seven (18%) were "zero-dose" children, and 17 (45%) were children reported to have received ≥4 doses of OPV.

WPV and cVDPV Genomic Sequence Analysis

Analysis of the nucleotide sequence of the VP1 region of all WPV and cVDPV2 isolates is used to investigate transmission links, track international spread, and assess both viral diversity as a measure of circulation intensity and surveillance sensitivity (9).†† After a substantial decline in the genetic diversity (reflected by the number of genetic clusters) of WPV1 strains from 21 clusters in 2009 to four clusters in 2010, the number of clusters increased to eight in 2011. The number of WPV3 clusters declined from 21 in 2009 to six in 2010 and to four in 2011. Genomic sequence analysis shows much less genetic linkage than expected with sensitive AFP surveillance, including some chains of WPV transmission during 2011–2012 not detected for more than a year. The proportion of WPV and cVDPV2 isolates (from cases and contacts) with less than expected genetic linkage (>98.5%) was 60% (29 of 48) in 2010, 31% (30 of 98) in 2011, and 16% (16 of 103) to date in 2012.

Reported by

National Primary Health Care Development Agency and Federal Ministry of Health; World Health Organization Country Office, Abuja; Poliovirus Laboratory, Univ of Ibadan, Ibadan; Poliovirus Laboratory, Univ of Maiduguri Teaching Hospital, Maiduguri, Nigeria. African Regional Polio Reference Laboratory, National Institute for Communicable Diseases, Johannesburg, South Africa. Immunization and Vaccine Development, World Health Organization Regional Office for Africa, Brazzaville, Congo; Polio Eradication Dept, World Health Organization, Geneva, Switzerland. Div of Viral Diseases, National Center for Immunization and Respiratory Diseases; Global Immunization Div, Center for Global Health, CDC. Corresponding contributor: Stacie Dunkle, Global Immunization Div, Center for Global Health, CDC; [email protected]; 404-861-4841.

Editorial Note

Indigenous WPV1 and WPV3 transmission has continued in the northern states of Nigeria because of long-standing weaknesses in health system infrastructure, programmatic limitations in the planning and implementation of SIAs, and insufficient accountability, compounded by low public confidence in OPV since 2003 in some communities (10). By 2009, substantial progress in implementation of polio eradication activities (attributed to enhanced collaboration with traditional, religious, and political leaders) was followed by a sharp decline in cases; however, a substantial proportion of children, including each newborn cohort, remained chronically unvaccinated or undervaccinated. As WPV continues to circulate in multiple "sanctuaries"§§ in northern states (7), WPV1 and WPV3 cases have increased since 2010, with cases occurring in a growing number of LGAs. Only 17 WPV3 cases were reported in Nigeria during January–September 2012, but WPV3 strains in Nigeria are more genetically diverse than WPV3 strains in Pakistan, the only other country with circulating WPV3 in 2012 (4). Cases of cVDPV2 have declined in 2012; however, extensive cVDPV2 circulation continues to be detected by environmental surveillance in Sokoto.

Although subnational AFP surveillance indicators generally are being met and sequence analysis suggests some improvement in sensitivity over time, environmental surveillance and genomic sequence evidence indicate that substantial surveillance gaps persist (5,9); these gaps might result from variability in AFP surveillance sensitivity at the LGA level or within population subgroups. Key challenges to achieving the high routine and supplementary vaccination coverage that is required to eliminate poliovirus transmission in Nigeria remain and have been compounded by insecurity in some states since late 2011. To address these challenges, the Nigeria 2012 Polio Eradication Emergency Plan (6) includes new initiatives to enhance high-level political oversight and improve program management and accountability, and provides for the deployment of a surge in human resources by government and partner organizations (primarily the World Health Organization and the United Nations Children's Fund) in high-risk states, down to the lowest administrative levels (wards). The augmented technical staff is implementing new strategies to reach chronically missed children during SIAs; these include the use of revised, detailed, and extensively validated house-to-house SIA microplans, more rigorous selection and training of vaccinators, revision of the size and composition of vaccination teams, and increased attention to the identification and vaccination of nomadic and other vulnerable populations. In some states, satellite mapping improved the demarcation of LGA, ward, and team boundaries and identified previously missed settlements. Volunteer community mobilizers have been deployed to settlements with historically high vaccination refusal rates. Insecurity in some LGAs in Borno and Yobe states creates difficulties in reaching undervaccinated children; addressing this will require enhanced engagement of affected communities.

A Nigerian presidential task force was established in March 2012 to provide leadership and oversight of state and local task forces and to improve local accountability for implementation of SIAs. An accountability "dashboard" tool¶¶ has been developed and implemented for monitoring SIA preparations and execution at the LGA level. In addition, experienced Indian surveillance medical officers and a National Stop Transmission of Polio program of health professionals have been deployed to support the development of sustainable management capacity in high-risk LGAs. Efforts continue to identify and include nomadic and otherwise vulnerable children in current microplans, strengthen SIA supervision, and enhance community awareness and availability of routine vaccination through outreach services. The epidemiologic impact of the recent implementation of the Polio Eradication Emergency Plan has yet to be observed; however, improvements in SIA coverage are establishing a stronger footing for measurable progress in 2013. If WPV case counts and extent of circulation are not reduced substantially by mid-2013, additional innovative vaccination strategies to interrupt all WPV transmission will need to be considered. Ongoing WPV transmission in northern Nigeria remains a threat for reintroduction into southern Nigeria and surrounding polio-free countries in Africa, and is a major obstacle to success of GPEI (7).

References

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8. World Health Organization. WHO vaccine-preventable diseases monitoring system: 2012 global summary. Geneva, Switzerland: World Health Organization; 2012. Available at http://www.who.int/vaccines/globalsummary/immunization/countryprofileselect.cfm. Accessed November 1, 2012.
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10. CDC. Progress toward poliomyelitis eradication—Nigeria, January 2004–July 2005. MMWR 2005;54:873–7.