• Giedre Gefenaite, Margot Tacken, Jens Bos, Irina Stirbu-Wagner, Joke C Korevaar, Ronald P Stolk, Bert Wolters, Marc Bijl, Maarten J Postma, Jan Wilschut, Kristin L Nichol, and Eelko Hak.
• Department of Pharmacy, Unit of PharmacoEpidemiology & PharmacoEconomics (PE2), University of Groningen, Groningen, The Netherlands. g.gefenaite@umcg.nl
• Plos One. 2013 Jan 1; 8 (6): e66125.

IntroductionBecause of variability in published A(H1N1)pdm09 influenza vaccine effectiveness estimates, we conducted a study in the adults belonging to the risk groups to assess the A(H1N1)pdm09 MF59-adjuvanted influenza vaccine effectiveness.MethodsVE against influenza and/or pneumonia was assessed in the cohort study (n>25000), and vaccine effectiveness against laboratory-confirmed A(H1N1)pdm09 influenza was assessed in a matched case-control study (16 pairs). Odds ratios (OR) and their 95% confidence intervals (95% CI) were calculated by using multivariate logistic regression; vaccine effectiveness was estimated as (1-odds ratio)*100%.ResultsVaccine effectiveness against laboratory-confirmed A(H1N1)pdm09 influenza and influenza and/or pneumonia was 98% (84-100%) and 33% (2-54%) respectively. The vaccine did not prevent influenza and/or pneumonia in 18-59 years old subjects, and was 49% (16-69%) effective in 60 years and older subjects.ConclusionsEven though we cannot entirely rule out that selection bias, residual confounding and/or cross-protection has played a role, the present results indicate that the MF59-adjuvanted A(H1N1)pdm09 influenza vaccine has been effective in preventing laboratory-confirmed A(H1N1)pdm09 influenza and influenza and/or pneumonia, the latter notably in 60 years and older subjects.

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