Progress Toward Poliomyelitis Eradication --- Nigeria, January 2007--August 12, 2008

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Nigeria is one of only four countries that have never interrupted poliovirus transmission (the others are Afghanistan, India, and Pakistan). A resurgence in wild poliovirus (WPV) transmission occurred in Nigeria during 2003--2004 after a loss of public confidence in oral poliovirus vaccine (OPV) and suspension of supplementary immunization activities (SIAs)* in several northern states (1). Subsequently, WPV spread within Nigeria and ultimately into 20 previously polio-free countries during 2003--2006 (2--4). Even after national SIAs resumed, limited acceptance and ongoing operational problems resulted in low polio vaccination coverage and continued WPV transmission. Beginning in 2006, health authorities in Nigeria introduced new initiatives to control the spread of WPV, including a focus on interrupting type 1 WPV (WPV1) transmission and use of monovalent type 1 OPV (mOPV1) for most of the SIAs to increase vaccine effectiveness. Nigeria also instituted changes in SIA implementation to increase community acceptance of vaccination (5). Subsequently, 285 polio cases were reported in Nigeria in 2007, the lowest number since sensitive surveillance has been in place (2). As of August 12, 2008, confirmed polio cases reported in Nigeria totaled 556 (including 511 WPV1 cases), compared with 176 cases (53 WPV1) reported during the same period in 2007. This report updates (5) overall progress toward polio eradication in Nigeria during 2007--2008. Given the increase in WPV transmission thus far in 2008, urgent measures are needed to reach all children during SIAs to bring WPV under control in Nigeria.

Immunization Activities

Through a program of enhanced health-worker training and supervision and community outreach begun in 2006, Nigeria was able to improve routine vaccination coverage (5). National reported routine vaccination coverage for 3 doses of trivalent OPV (tOPV) among infants increased from 32% (range by state: 10%--57%) in 2005 to an average of 62% in 2007 (range by state: 30% to >100%^§), with the lower range of coverage reported from some northern states. In addition to lower average coverage, the highest proportion of local government areas (LGAs) with reported coverage <30% was in selected northern states. Substantial problems remain in providing primary health care and immunization services in these states.

The Nigerian government first used mOPV1 in March 2006 (Figure 1), following a national tOPV SIA in February 2006. In May 2006, the government introduced a modified strategy of SIA implementation, called immunization plus days (IPDs), during which OPV and other health interventions (e.g., other vaccines, anthelminthics, and insecticide-treated bednets) were delivered at fixed sites, combined with providing OPV through house-to-house delivery (5). Subsequent SIAs in 2006 were implemented as subnational IPDs in states with confirmed WPV transmission; three subnational IPDs were held using mOPV1 and one using tOPV. In January 2007, a national IPD used tOPV in northern states and mOPV1 in the south (Table). Of six subnational IPDs in affected areas during 2007, two used tOPV alone, three primarily used mOPV1 alone, and one used mOPV3 alone. In addition, five smaller mop-up SIAs using the best-matched vaccine were conducted in response to recent local WPV circulation.

In 2008, as of August 12, two national IPDs (one using mOPV1, the other mOPV3) and three subnational IPDs had been conducted (primarily using mOPV1) (Table). During late 2007 and early 2008, state funding delays and logistical problems resulted in limited availability of other vaccines and health interventions in IPDs in some areas. One innovation introduced in May 2008 was to implement subnational SIAs using a staggered approach, beginning in states at highest risk and followed by campaigns in other states about a week later, to better supervise campaign preparation and implementation. An additional mOPV1 SIA was planned for late August in the northern states. Measles campaigns planned for northern states in November and for southern states in December also will include mOPV1 administered to target children at fixed sites. During December, several northern states with high incidence of polio also plan to conduct additional SIAs with mOPV1.

Vaccination histories of children aged 6--59 months with nonpolio acute flaccid paralysis (AFP) are used to estimate OPV coverage of the overall target population. Because of lower routine vaccination coverage in areas with high polio incidence, and despite repeated SIAs, the proportion of zero-dose children (thosewhose parents reported that they had never been vaccinated with OPV) remained substantially higher in polio-affected areas (18%) in Nigeria than in polio-free areas (2%) in 2007 (2). In seven high-incidence^¶ northern states (Bauchi, Jigawa, Kano, Kaduna, Katsina, Yobe, and Zamfara), the proportion of zero-dose children decreased from 45% by quarter in early 2006 to 30% in early 2007, but the proportion had not fallen below 25% as of August 12, 2008.

Acute Flaccid Paralysis (AFP) Surveillance

The polio eradication initiative relies on surveillance of AFP to identify cases of poliomyelitis; AFP surveillance is monitored according to World Health Organization (WHO) operational targets for case detection and adequate stool specimen collection.** In 2007, the national nonpolio AFP detection rate decreased to 5.9 cases per 100,000 population aged <15 years compared with 7.9 cases per 100,000 children in 2006. In 2007, all 37 states and 85% of the 774 LGAs achieved nonpolio AFP rates that met the target of >2 cases per 100,000, similar to the performance in 2006. In 2007, adequate stool specimens were collected for 91.6% of AFP cases nationally, an increase from 86.4% in 2006. In 2007, all 37 states and 85% of LGAs reached the target of >80% of AFP cases with adequate stool specimens, compared with 84% of states and 75% of LGAs in 2006. The proportion of LGAs that reached the target levels for both surveillance indicators increased from 64% in 2006 to 84% in 2007. Large gaps in the genetic relatedness of WPV isolates measured by genomic sequence analysis continue to indicate problems with surveillance sensitivity, possibly the result of decreased AFP case detection, limitations in specimen collection, or lapses in specimen transportation conditions.

WPV Incidence

Of the 841 WPV cases reported during 2007--2008, a total of 622 (74%) occurred in children aged <3 years; 543 (65%) of cases were in children who were reported to have received <3 doses of OPV, and 224 cases (27%) were in children who were reported to have received no OPV doses.

Of the 285 WPV polio cases with onset in 2007 (116 WPV1 and 169 WPV3), a total of 60 (21%) were reported from Kano state (11 WPV1 and 49 WPV3), and 114 (40%) (44 WPV1 and 70 WPV3) were reported from six other high-incidence states. Of the 556 polio cases (511 WPV1 and 45 WPV3) with onset in 2008, as of August 12, 194 (35%) (190 WPV1 and 4 WPV3) were from Kano state, and 248 (45%) (227 WPV1 and 21 WPV3) were from the other six high-incidence states. In 2006, 18 (49%) of Nigeria's 37 states were affected; that increased to 23 (62%) affected states in 2007 and 23 affected states thus far in 2008. In 2007, the first WPV3 cases since 2004 were reported from southern Nigeria and in 2008, the first WPV1 cases since 2005 were reported from this area. Although the decrease in WPV1 incidence during 2007 was most pronounced in the seven northern states that had the highest incidence of poliomyelitis in 2006 (5), a resurgence in the disease, beginning in the second half of 2007 in these same states and in additional northern states, led to the increased case numbers in 2008. The number of WPV1-affected LGAs in 2008 to date is 180, an increase from 40 reported during the same period in 2007 (Figure 2). The total number of WPV1-affected LGAs during all of 2007 was 78. The number of WPV3-affected LGAs in 2008 to date is 37, a decrease from 77 reported during the same period in 2007. The total number of WPV3-affected LGAs during 2007 was 108.

WPV1 and WPV3 isolated from persons with polio cases in Chad and eastern Niger during 2007--2008 were closely related to viruses found in nearby Nigerian states. Circulation of WPV3 has been ongoing in Chad, after WPV introduction from Nigeria in 2007. Isolated cases of WPV3 and WPV1 occurred in Niger in 2007 and of WPV1 in 2008. In some instances, local WPV1 transmission occurred after introduction from Nigeria during this period (2). In 2008, as of August 12, individual cases of WPV1 of Nigerian origin have been reported in Benin and western Niger, close to Niger's borders with Mali and Burkina Faso, and more recently in Burkina Faso itself (6).

Reported by: National Primary Health Care Development Agency and 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, Brazzaville, Congo. Immunization, Vaccines, and Biologicals Dept, World Health Organization, Geneva, Switzerland. Div of Viral Diseases and Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

After the introduction of mOPV1 and IPDs in early 2006, some progress was made in Nigeria toward the goal to interrupt WPV1 transmission (2). Community acceptance of OPV in response to the IPDs seemed to improve: the proportion of zero-dose children in high-incidence states decreased, and the number of WPV1 cases and affected districts at the end of 2006 and during 2007 decreased substantially (2,5). However, improvements have not been sufficient to prevent renewed WPV1 transmission in high-incidence northern states because of high birth rates, continued low routine immunization coverage, and less than optimal OPV coverage during SIAs.

Nigeria accounts for 88% of the 575 WPV1 cases reported globally during January 1--August 12, 2008. More WPV1 cases have been reported to date during 2008 than all WPV cases in the entire previous year, and both WPV1 and WPV3 have reemerged in some southern states. In addition, type 2 vaccine-derived poliovirus emerged in 2005--2006 and continues to circulate in northern Nigeria, causing a total of 103 vaccine-derived polio cases during January 1, 2007--August 12, 2008, in addition to the 841 confirmed WPV cases, and despite multiple tOPV SIAs (7). Such circulation reflects the historically long-standing, weak status of routine immunization services in these states. Recent WPV1 cases in Benin, western Niger, and Burkina Faso have again raised the threat of increased international transmission of WPV1 from Nigeria during 2008 (3,6).

In May 2008, the World Health Assembly reviewed reported progress in the Global Polio Eradication Initiative and noted the upsurge in cases in Nigeria and the substantial achievements in interrupting the transmission of WPV1 in India (2). The World Health Assembly took the unusual step of urging the Nigerian government to take immediate steps to reduce the risk for international spread of poliovirus through intensified eradication activities that ensure all children are vaccinated (2,8). Subsequently, the Minister of Health of Nigeria established a steering committee to improve governance in implementation of activities in Nigeria and cross-border SIA efforts. The Nigerian government also established a task force, headed by the Director of Public Health in the Ministry of Health, which will ensure that the directives of the steering committee are implemented. Because up to 30% of the target population in high-incidence states remains unvaccinated, further substantial improvements are needed in community acceptance and SIA operational implementation. Enhanced involvement of traditional and religious community leaders will be essential to increase both SIA and routine vaccination coverage and political accountability for implementation.

Among the four countries that have never interrupted poliovirus transmission, substantial progress has been made in India towards interruption of WPV1 and controlling WPV3 (2). West of India, in Afghanistan and Pakistan, interrupting WPV1 and WPV3 transmission in the areas with threats to security remains difficult (2,9). The Nigerian government and its immunization partners^§§have reaffirmed their commitment to interrupting WPV transmission as soon as possible through new innovations, and to building sustainable means of enhancing child health in Nigeria. Although improvement of routine immunization services in primary health care is a goal of all partners, much more urgent efforts to reach all children during SIAs are necessary to control the recent upsurge in cases and to interrupt WPV1, and subsequently WPV3, transmission in Nigeria.

References

* Mass campaigns conducted during a short period (days to weeks) during which a dose of OPV is administered to all children aged <5 years, regardless of previous vaccination history. Campaigns can be conducted nationally or in portions of the country.

WPV1 is more likely to cause paralytic disease and have a wider geographic spread than WPV3; monovalent poliovirus vaccines are more effective against a given WPV type than trivalent OPV (tOPV).

^§Proportions exceeding 100% can occur in administrative data as a result of errors in recording vaccination numbers and errors in estimating target population numbers; administrative data therefore are not as reliable as data collected from actual coverage surveys.

^¶Incidence rate of confirmed polio cases per 100,000 children aged <5 years was >5.0 in 2006 and in 2008 (annualized).

**AFP cases in all children aged <15 years and suspected polio in persons of any age are reported and investigated, with laboratory testing, as possible poliomyelitis. The current WHO operational targets for countries at high risk for polio transmission are a nonpolio AFP rate of at least two cases per 100,000 population aged <15 years at each subnational level and adequate stool specimen collection for >80% of AFP cases (i.e., two specimens collected at least 24 hours apart, both within 14 days of paralysis onset, and shipped on ice or frozen ice packs to a WHO-accredited laboratory and arriving at the laboratory in good condition).

^§§National Primary Health Care Development Agency, Nigeria Federal Ministry of Health, Association of Local Governments of Nigeria, Nigerian state governments, World Health Organization, Rotary International, CDC, United Nations Children's Fund (UNICEF), European Union, the Bill and Melinda Gates Foundation, the Global Alliance for Vaccines and Immunization, The Vaccine Fund, and bilateral development agencies of Canada, Norway, Japan, the United Kingdom, and the United States (U.S. Agency for International Development [USAID]).

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