Outbreak of Type 2 Vaccine-Derived Poliovirus in Nigeria: Emergence and Widespread Circulation in an Underimmunized Population

Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
The Journal of Infectious Diseases (Impact Factor: 6). 04/2011; 203(7):898-909. DOI: 10.1093/infdis/jiq140
Source: PubMed


(See the article by Nathanson et al., on pages 889–90.)

Wild poliovirus has remained endemic in northern Nigeria because of low coverage achieved in the routine immunization program
and in supplementary immunization activities (SIAs). An outbreak of infection involving 315 cases of type 2 circulating vaccine-derived
poliovirus (cVDPV2; >1% divergent from Sabin 2) occurred during July 2005–June 2010, a period when 23 of 34 SIAs used monovalent
or bivalent oral poliovirus vaccine (OPV) lacking Sabin 2. In addition, 21 “pre-VDPV2” (0.5%–1.0% divergent) cases occurred
during this period. Both cVDPV and pre-VDPV cases were clinically indistinguishable from cases due to wild poliovirus. The
monthly incidence of cases increased sharply in early 2009, as more children aged without trivalent OPV SIAs. Cumulative state
incidence of pre-VDPV2/cVDPV2 was correlated with low childhood immunization against poliovirus type 2 assessed by various
means. Strengthened routine immunization programs in countries with suboptimal coverage and balanced use of OPV formulations
in SIAs are necessary to minimize risks of VDPV emergence and circulation.

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    • "As in Bihar and WUP, we assume that approximately 10% of the Northwest zone remains chronically under-vaccinated and preferentially mixes with itself to sustain indigenous WPV transmission even when the general population became better-immunized [20]. The model focuses on reproducing the pattern of endemic circulation and elimination of all three WPVs as well as the large and prolonged type 2 cVDPV outbreak that started around 2005 [30] (see Additional file 1). The reference case represents continuation of the status quo from 2013 forward, assuming continued true coverage of 0.85, repeated missed probability of 0.85, and relative coverage of 0.2 in the subpopulation at the level reached in late-2013 in the retrospective model. "
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