Factors Contributing to Outbreaks of Wild Poliovirus Type 1 Infection Involving Persons Aged ≥15 Years in the Democratic Republic of the Congo, 2010-2011, Informed by a Pre-Outbreak Poliovirus Immunity Assessment

Background. The Democratic Republic of the Congo (DRC) experienced atypical outbreaks of wild poliovirus type 1 (WPV1) infection during 2010-2011 in that they affected persons aged >= 15 years in 4 (Bandundu, Bas Congo, Kasai Occidental, and Kinshasa provinces) of the 6 provinces with outbreaks. Methods.aEuro integral Analyses of cases of WPV1 infection with onset during 2010-2011 by province, age, polio vaccination status, and sex were conducted. The prevalence of antibodies to poliovirus (PV) types 1, 2, and 3 was assessed in sera collected before the outbreaks from women attending antenatal clinics in 3 of the 4 above-mentioned provinces. Results.aEuro integral Of 193 cases of WPV1 infection during 2010-2011, 32 (17%) occurred in individuals aged a parts per thousand yen15 years. Of these 32 cases, 31 (97%) occurred in individuals aged 16-29 years; 9 (28%) were notified in Bandundu, 17 (53%) were notified in Kinshasa, and 22 (69%) had an unknown polio vaccination status. In the seroprevalence assessment, PV type 1 and 3 seroprevalence was lower among women aged 15-29 years in Bandundu and Kinshasa, compared with those in Kasa < Occidental. Seropositivity to PVs was associated with increasing age, more pregnancies, and a younger age at first pregnancy. Conclusions.aEuro integral This spatiotemporal analysis strongly suggests that the 2010-2011 outbreaks of WPV1 infection affecting young adults were caused by a PV type 1 immunity gap in Kinshasa and Bandundu due to insufficient exposure to PV type 1 through natural infection or vaccination. Poliovirus immunity gaps in this age group likely persist in DRC.