title: Effectiveness of oral polio vaccination against paralytic poliomyelitis: a matched case-control study in Somalia.
abstract: 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.
  
  
  RESULTS
  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.
authors.affiliation: Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Abdirahman
authors.initials: A
authors.lastname: Mahamud
authors.affiliation: Somalia Country Office, World Health Organization (WHO).
authors.forename: Raoul
authors.initials: R
authors.lastname: Kamadjeu
authors.affiliation: Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Jenna
authors.initials: J
authors.lastname: Webeck
authors.affiliation: Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Chukwuma
authors.initials: C
authors.lastname: Mbaeyi
authors.affiliation: United Nations Children's Fund (UNICEF), Somalia Support Centre, Nairobi, Kenya.
authors.forename: Marie Therese
authors.initials: MT
authors.lastname: Baranyikwa
authors.affiliation: United Nations Children's Fund (UNICEF), Somalia Support Centre, Nairobi, Kenya.
authors.forename: Julianne
authors.initials: J
authors.lastname: Birungi
authors.affiliation: Somalia Ministry of Human Development and Public Services, Health Directorate, Mogadishu.
authors.forename: Yassin
authors.initials: Y
authors.lastname: Nurbile
authors.affiliation: Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Derek
authors.initials: D
authors.lastname: Ehrhardt
authors.affiliation: Global Polio Eradication Initiative, WHO, Geneva, Switzerland.
authors.forename: Hemant
authors.initials: H
authors.lastname: Shukla
authors.affiliation: United Nations Children's Fund (UNICEF), Somalia Support Centre, Nairobi, Kenya.
authors.forename: Anirban
authors.initials: A
authors.lastname: Chatterjee
authors.affiliation: Somalia Country Office, World Health Organization (WHO).
authors.forename: Abraham
authors.initials: A
authors.lastname: Mulugeta
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011051:Poliomyelitis / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D017955:Poliovirus / Q000302:isolation & purification*; D011055:Poliovirus Vaccine, Oral / Q000008:administration & dosage* / Q000276:immunology*; D012189:Retrospective Studies; D012998:Somalia / Q000453:epidemiology; D016896:Treatment Outcome; D014611:Vaccination / Q000379:methods* / Q000706:statistics & numerical data
chemical_list: D011055:Poliovirus Vaccine, Oral
keywords: Somalia; oral polio vaccine; vaccine effectiveness