Influenza vaccination and mortality in the elderly

BACKGROUND AND OBJECTIVE: Though there is a general agreement on the need of influenza vaccination (IV), very different results have been published about the magnitude of its effect. We evaluated the effectiveness of IV in the reduction of mortality in individuals over 65 years of age. PATIENTS AND METHOD: Prospective cohort study of all individuals over 65 attended in 8 urban primary care centers (n = 11,241). We assessed IV in autumn 2001 and considered the death from all causes during 2002 as a response variable. We calculated the global effectiveness (1- relative risk) and the necessary number of vaccinations in order to prevent 1 death (NNT = 1/attributable risk). RESULTS: Global effectiveness of IV was 2%, considering an NNT of 1667. No vaccination benefit among the 65-74 years-old group was observed, but IV proved 22% effectiveness (95% confidence interval, 3-38%) in individuals over 75, with an estimated NNT of 66 vaccinations (95% confidence interval, 38-435). CONCLUSIONS: Within a year with a moderate incidence of influenza, IV had a small effectiveness in preventing general mortality in our area, though it was especially effective among those at higher risk (over 75 and suffering from chronic pathologies).