Impact of influenza vaccination on mortality in the French elderly population during the 2000-2009 period.

With declining influenza vaccine coverage in the elderly in recent years in France, we aimed at assessing the benefits of seasonal influenza vaccination, based on available data for observed mortality, vaccine coverage and vaccine effectiveness. To estimate the annual number of deaths avoided by vaccination in the people aged 65 years or more, we used the following three elements: an estimate of vaccine effectiveness against all-cause mortality (based on the "difference-in-differences" approach which reduces the usual bias seen in observational studies), French mortality data and vaccine coverage data. We estimated an annual average of 2000 deaths currently avoided through vaccination and a vaccine effectiveness of 35% against influenza-attributable deaths. Around 2650 vaccinations are needed to prevent a death among the elderly. Communicating these results should help restoring at-risk populations' confidence in influenza vaccination.