Effectiveness of Oral Polio Vaccination Against Paralytic Poliomyelitis: A Matched Case-Control Study in Somalia

• Published in: The Journal of infectious diseases Vol. 210; no. suppl 1; pp. S187 - S193
• Main Authors: Mahamud, Abdirahman, Kamadjeu, Raoul, Webeck, Jenna, Mbaeyi, Chukwuma, Baranyikwa, Marie Therese, Birungi, Julianne, Nurbile, Yassin, Ehrhardt, Derek, Shukla, Hemant, Chatterjee, Anirban, Mulugeta, Abraham
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.11.2014
• Subjects: Adolescent; Age; Case control studies; Child; Child, Preschool; Control groups; Disease eradication; Disease Outbreaks; EASTERN MEDITERRANEAN REGION; Female; Health surveillance; Humans; Infant; Infant, Newborn; Male; Oral poliovirus vaccines; Paralysis; Poliomyelitis; Poliomyelitis - epidemiology; Poliomyelitis - immunology; Poliomyelitis - prevention & control; Poliomyelitis - virology; Poliovirus - isolation & purification; Poliovirus Vaccine, Oral - administration & dosage; Poliovirus Vaccine, Oral - immunology; Poliovirus vaccines; Preventive medicine; Retrospective Studies; Somalia - epidemiology; Treatment Outcome; Vaccination - methods; Vaccination - statistics & numerical data; Somalia; vaccine effectiveness; oral polio vaccine; Somalia
• ISSN: 0022-1899; 1537-6613
• DOI: 10.1093/infdis/jiu261

Background. After the last case of type 1 wild poliovirus (WPV1) was reported in 2007, Somalia experienced another outbreak of WPV1 (189 cases) in 2013. Methods. We 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. Result. We 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. Conclusions. Among individuals who were fully vaccinated with OPV, vaccination was effective at preventing WPV1 in Somalia.