First estimates of influenza vaccine effectiveness among severe influenza cases, France, 2011/12

Following a suspected virus-vaccine mismatch, the screening method was used to estimate in almost real time the influenza vaccine effectiveness (VE) against severe cases in high-risk individuals. Data on vaccination status were provided by the influenza severe surveillance system and data on vaccination coverage by the National Social Security Scheme. The analysis showed a decline of the vaccine effectiveness in 2011/12 (VE: 30% (95% CI: 22-39)) compared to 2010/11 (VE: 53% (95% CI: 40-67)).