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

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

Household survey analysis of the impact of comprehensive strategies to improve the expanded programme on immunisation at the county level in western China, 2006–2010

Objective To evaluate interventions to improve routine vaccination coverage and caregiver knowledge in China's remote west, where routine immunisation is relatively weak. Design Prospective pre-post (2006-2010) evaluation in project counties; retrospective comparison based on 2004 administrative data at baseline and surveyed post-intervention (2010) data in selected non-project counties. Setting Four project counties and one non-project county in each of four provinces. Participants 3390 children in project counties at baseline, and 3299 in project and 830 in non-project counties post-intervention; and 3279 caregivers at baseline, and 3389 in project and 830 in non-project counties post-intervention. Intervention Multicomponent inexpensive knowledge-strengthening and service-strengthening and innovative, multisectoral engagement. Data collection Standard 30-cluster household surveys of vaccine coverage and caregiver interviews pre-intervention and post-intervention in each project county. Similar surveys in one non-project county selected by local authorities in each province post-intervention. Administrative data on vaccination coverage in non-project counties at baseline. Primary outcome measures Changes in vaccine coverage between baseline and project completion (2010); comparative caregiver knowledge in all counties in 2010. Analysis Crude ((2)) analysis of changes and differences in vaccination coverage and related knowledge. Multiple logistic regression to assess associations with timely coverage. Results Timely coverage of four routine vaccines increased by 21% (p<0.001) and hepatitis B (HepB) birth dose by 35% (p<0.001) over baseline in project counties. Comparison with non-project counties revealed secular improvement in most provinces, except new vaccine coverage was mostly higher in project counties. Ethnicity, province, birthplace, vaccination site, dual-parental out-migration and parental knowledge had significant associations with coverage. Knowledge increased for all variables but one in project counties (highest p<0.05) and was substantially higher than in non-project counties (p<0.01). Conclusions Comprehensive but inexpensive strategies improved vaccination coverage and caretaker knowledge in western China. Establishing multisectoral leadership, involving the education sector and including immunisation in public-sector performance standards, are affordable and effective interventions.UNICEF ChinaSCI(E)[email protected]; [email protected]