Pandemic Influenza Vaccine Effectiveness in Europe in 2009-10: Results of I-MOVE Multicentre Case-Control Study

Background: Following the emergence of the 2009 pandemic influenza A(H1N1) virus, monovalent influenza vaccines were developed and marketed in Europe. Within the Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) project, we estimated the pandemic influenza vaccines effectiveness (PIVE) using sentinel general practitioners (GP) influenza surveillance networks in seven European countries.

Methods: We conducted a multicentre case-control study between November 2009 and March 2010. Using systematic sampling, GPs swabbed patients presenting with influenza-like illness (ILI European Union case definition) within eight days of symptom onset and collected their vaccination history and a list of potential confounders (e.g. age group, chronic diseases and related hospitalisations, seasonal influenza vaccination). Cases were ILI patients with laboratory-confirmed pandemic influenza. Controls were ILI patients testing negative for influenza. Vaccination was defined as having received one dose of vaccine more than 14 days before symptom onset. We used multiple imputation with chained equations to estimate missing values. We computed adjusted PIVE as [1-OR] using logistic regression with study site as fixed effect.

Results: Overall, 699 GPs participated in the study. We included 918 cases and 1984 controls in the analysis. The median age was 12 years in cases and 27 years in controls. Twelve cases (1.3%) and 185 controls (9.3%) had been vaccinated against pandemic influenza.The adjusted PIVE was 71.9% (95%CI:45.6-85.5) overall, 78.4% (95%CI:54.4-89.8) among those <65 years and 72.9 (95%CI:39.8-87.8) in those without chronic diseases.

Conclusions: Our results suggest that pandemic vaccines offered good protection against medically-attended ILI pandemic influenza. Despite the low vaccine coverage in Europe, pooling of data enabled to reach a sufficient sample size to obtain precise estimates. Our results are an important adjunct to the clinical trials to guide vaccination policies.

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Author (s): 

Anne-Sophie Barret, E. Kissling, M. Valenciano, JM. Cohen, B. Oroszi, C. Rizzo, B. Nunes, D. Pitigoi, A. Larrauri, A. Mosnier, JK. Horvath, J. O?Donnell, A. Bella, R. Guiomar, E. Lupulescu, C. Savulescu, BC. Ciancio, P. Kramarz, A. Moren

Presenter (s): 
Ms. Anne-Sophie Barret
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