Measles outbreak reveals measles susceptibility among adults in Namibia, 2009-2011

Type Journal Article - SAMJ: South African Medical Journal
Title Measles outbreak reveals measles susceptibility among adults in Namibia, 2009-2011
Volume 106
Issue 7
Publication (Day/Month/Year) 2016
Page numbers 715-720
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.
Conclusion. 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.

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