Low vaccine effectiveness against influenza A(H3N2) virus among elderly people in Denmark in 2012/13 – a rapid epidemiological and virological assessment

K Bragstad; H D Emborg; T K Fischer; M Voldstedlund; S Gubbels; B Andersen; K Mølbak; T G Krause

doi:10.2807/ese.18.06.20397-en

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Low vaccine effectiveness against influenza A(H3N2) virus among elderly people in Denmark in 2012/13 – a rapid epidemiological and virological assessment
K Bragstad^1,2 , H D Emborg^2,3 , T K Fischer¹ , M Voldstedlund³ , S Gubbels ³ , B Andersen¹ , K Mølbak³ , T G Krause³
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Affiliations: ¹ National Influenza Centre, Department of Microbiological Diagnostics and Virology, Statens Serum Institut, Copenhagen, Denmark ² These authors contributed equally to the work and share first authorship ³ Department of Infectious Disease Epidemiology, Statens Serum Institut, Copenhagen, Denmark

Correspondence:
T Krause
TGV ssi.dk
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Citation style for this article: Bragstad K, Emborg H D, Fischer T K, Voldstedlund M, Gubbels S, Andersen B, Mølbak K, Krause T G. Low vaccine effectiveness against influenza A(H3N2) virus among elderly people in Denmark in 2012/13 – a rapid epidemiological and virological assessment. Euro Surveill. 2013;18(6):pii=20397. https://doi.org/10.2807/ese.18.06.20397-en Received: 29 Jan 2013

Abstract

In Denmark, the 2012/13 influenza season has been dominated by influenza A(H3N2). We estimated the vaccine effectiveness (VE) of the trivalent influenza vaccine by linking national registers in a test-negative case-control study of patients tested for influenza aged ≥65 years. The adjusted VE against laboratory-confirmed influenza A and B was -11% (95% CI: -41 to 14) and 69% (95% CI: 26 to 87), respectively. Genetic characterisation of the influenza A(H3N2) viruses indicated genetic drift, with seven substitutions at key antigenic sites. .