title: Measles outbreak reveals measles susceptibility among adults in Namibia, 2009 - 2011.
abstract: BACKGROUND
  The World Health Organization, African Region, set the goal of achieving measles elimination by 2020. Namibia was one of seven African countries to implement an accelerated measles control strategy beginning in 1996. Following implementation of this strategy, measles incidence decreased; however, between 2009 and 2011 a major outbreak occurred in Namibia.
  
  
  METHODS
  Measles vaccination coverage data were analysed and a descriptive epidemiological analysis of the measles outbreak was conducted using measles case-based surveillance and laboratory data.
  
  
  RESULTS
  During 1989 - 2008, MCV1 (the first routine dose of measles vaccine) coverage increased from 56% to 73% and five supplementary immunisation activities were implemented. During the outbreak (August 2009 - February 2011), 4 605 suspected measles cases were reported; of these, 3 256 were confirmed by laboratory testing or epidemiological linkage. Opuwo, a largely rural district in north-western Namibia with nomadic populations, had the highest confirmed measles incidence (16 427 cases per million). Infants aged ≤11 months had the highest cumulative age-specific incidence (9 252 cases per million) and comprised 22% of all confirmed cases; however, cases occurred across a wide age range, including adults aged ≥30 years. Among confirmed cases, 85% were unvaccinated or had unknown vaccination history. The predominantly detected measles virus genotype was B3, circulating in concurrent outbreaks in southern Africa, and B2, previously detected in Angola.
  
  
  CONCLUSIONS
  A large-scale measles outbreak with sustained transmission over 18 months occurred in Namibia, probably caused by importation. The wide age distribution of cases indicated measles-susceptible individuals accumulated over several decades prior to the start of the outbreak.
authors.affiliation: Global Immunization Division, Center for Global Health, US Centers for Disease Control and Prevention, Atlanta, USA; Department of Immunization, Vaccines and Biologicals, World Health Organization, Geneva, Switzerland. ogbuanui@who.int.
authors.forename: Ikechukwu U
authors.initials: IU
authors.lastname: Ogbuanu
authors.forename: Clementine
authors.initials: C
authors.lastname: Muroua
authors.forename: Martiena
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authors.lastname: Allies
authors.forename: Kennedy
authors.initials: K
authors.lastname: Chitala
authors.forename: Sue
authors.initials: S
authors.lastname: Gerber
authors.forename: Primus
authors.initials: P
authors.lastname: Shilunga
authors.forename: Petrus
authors.initials: P
authors.lastname: Mhata
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Kriss
authors.forename: Lucille
authors.initials: L
authors.lastname: Caparos
authors.forename: Sheilagh B
authors.initials: SB
authors.lastname: Smit
authors.forename: Roselina J
authors.initials: RJ
authors.lastname: De Wee
authors.forename: James L
authors.initials: JL
authors.lastname: Goodson