• Abdirahman Mahamud, Raoul Kamadjeu, Jenna Webeck, Chukwuma Mbaeyi, Marie Therese Baranyikwa, Julianne Birungi, Yassin Nurbile, Derek Ehrhardt, Hemant Shukla, Anirban Chatterjee, and Abraham Mulugeta.
• Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
• J. Infect. Dis. 2014 Nov 1;210 Suppl 1:S187-93.

BackgroundAfter the last case of type 1 wild poliovirus (WPV1) was reported in 2007, Somalia experienced another outbreak of WPV1 (189 cases) in 2013.MethodsWe conducted a retrospective, matched case-control study to evaluate the vaccine effectiveness (VE) of oral polio vaccine (OPV). We retrieved information from the Somalia Surveillance Database. A case was defined as any case of acute flaccid paralysis (AFP) with virological confirmation of WPV1. We selected two groups of controls for each case: non-polio AFP cases ("NPAFP controls") matched to WPV1 cases by age, date of onset of paralysis and region; and asymptomatic "neighborhood controls," matched by age. Using conditional logistic regression, we estimated the VE of OPV as (1-odds ratio)×100.ResultWe matched 99 WPV cases with 99 NPAFP controls and 134 WPV1 cases with 268 neighborhood controls. Using NPAFP controls, the overall VE was 70% (95% confidence interval [CI], 37-86), 59% (2-83) among 1-3 dose recipients, 77% (95% CI, 46-91) among ≥4 dose recipients. In neighborhood controls, the overall VE was 95% (95% CI, 84-98), 92% (72-98) among 1-3 dose recipients, and 97% (89-99) among ≥4 dose recipients. When the analysis was limited to cases and controls ≤24 months old, the overall VE in NPAFP and neighborhood controls was 95% (95% CI, 65-99) and 97% (95% CI, 76-100), respectively.ConclusionsAmong individuals who were fully vaccinated with OPV, vaccination was effective at preventing WPV1 in Somalia.Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2014. This work is written by (a) US Government employee(s) and is in the public domain in the US.

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