Progress towards eradicating poliomyelitis in Nigeria, January 2007-August 2008 / Progres accomplis en vue de l'eradication de la poliomyelite au Nigeria, janvier 2007-aout 2008.

Nigeria (which in 2006 had a population of 140 million), is 1 of only 4 countries that have never interrupted poliovirus transmission (the others are Afghanistan, India and Pakistan). Nigeria has had to negotiate a complex course towards eradicating poliomyelitis. A resurgence in the transmission of wild poliovirus (WPV) occurred 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. (2,3,4) Even after national SIAs recommenced, limited acceptance and ongoing operational problems resulted in continued low polio vaccination coverage and continued WPV transmission. Beginning in 2006, health authorities in Nigeria introduced new initiatives, including the use of monovalent type-1 OPV (mOPV1) for most of the SIAs, to increase vaccine effectiveness and to focus on interrupting transmission of type-1 WPV (WPV1). (5) The government of Nigeria also instituted changes in SIA implementation to increase community acceptance of vaccination. (6) Subsequently, 285 polio cases were reported in Nigeria in 2007, the lowest number since sensitive surveillance was put in place in 2003. (2) However, despite the new initiatives introduced in 2006, OPV coverage in northern states has not been sufficient to prevent resurgence of poliovirus transmission during 2008. As of 12 August 2008, 556 confirmed cases of polio have been reported in Nigeria (511 WPV1) compared with 176 cases reported during the same period in 2007 (47 WPV1). This report updates previous information, (6) summarizes the overall progress made towards eradicating polio in Nigeria during 2007-2008 and provides an overview of plans to address resurgent WPV transmission in the country.

Immunization activities

Following renewed efforts in 2006 to improve routine immunization coverage through enhanced training and supervision of health-workers and improving community outreach, (6) the national reported coverage of routine vaccination with 3 doses of trivalent OPV (tOPV) among infants increased from 32% (range by state, 10% to 57%) in 2005 to an average of 62% in 2007 (range, 30% to 100%), with the lower range of coverage reported from some northern states. In addition to lower average coverage, the proportion of local government areas with reported coverage <30% was highest in selected northern states. Substantial problems remain in providing primary health care and immunization services in these states.

After a national SIA using tOPV in February 2006, the government of Nigeria first utilized mOPV1 in March 2006 (Fig. 1). In May 2006, the government introduced a modified strategy for SIA implementation, called immunization-plus days (IPDs), during which OPV and other health interventions (for example, other vaccines, anthelminthics, insecticide-treated bednets) were delivered using fixed-post vaccination combined with providing OPV through house-to-house delivery. (7) Subsequent SIAs in 2006 were implemented as subnational IPDs in states with confirmed WPV transmission; 3 IPDs were held using mOPV1 and 1 using tOPV. In 2007, 7 IPDs were conducted: a national IPD used tOPV in northern states and mOPV1 in the south; of 6 subnational IPDs in affected areas, 2 used only tOPV, 3 used mOPV1 alone and 1 used mOPV3 alone (Table 1). In addition, also in 2007, 5 smaller mop-up SIAs were conducted in response to local WPV circulation selectively using 1 of these vaccines. As of 12 August 2008, 2 national IPDs (one using mOPV1, the other mOPV3) and 3 subnational IPDs have been conducted (primarily using mOPV1) (Table 1). During late 2007 and early 2008, delays in state funding and logistical problems resulted in limited availability of other vaccines and health interventions during IPDs in some areas. In May 2008, an innovation was introduced implementing subnational SIAs through a staggered approach whereby immunization campaigns would begin first in highest risk states of the region, followed by campaigns in the rest of the states about 1 week later in order to better supervise preparation and implementation. An additional SIA delivering mOPV1 is planned for northern states in late August. Measles immunization campaigns planned for northern states (November) and southern states (December) will also include mOPV1 to target children at fixed sites. During early December, several high-risk northern states also plan to conduct additional SIAs delivering mOPV1.

[FIGURE 1 OMITTED]

Vaccination histories of children aged 6-59 months with non-polio acute flaccid paralysis (AFP) are used to estimate OPV coverage among the overall target population. Because of lower routine vaccination coverage in areas where there is a high incidence of polio, and despite repeated SIAs, the proportion of children whose parents reported that they had never been vaccinated with OPV ("zero-dose children"), remained substantially higher in 2007 in polio-affected areas (18%) in Nigeria than in polio-free areas (2%). (2) In 7 high-incidence northern states (8) (Bauchi, Jigawa, Kano, Kaduna, Katsina, Yobe and Zamfara), the proportion of zero-dose children decreased from 45% each quarter in early 2006 to 30% in early 2007 but has not fallen below 15% since late 2007.

Acute flaccid paralysis surveillance

The Polio Eradication Initiative relies on surveillance of AFP to identify cases of …