Influenza vaccination in the elderly: why are the overall benefits still hotly debated?

The exact magnitude of the benefit of influenza vaccine among elderly individuals is subject of considerable debated. Existing vaccine effectiveness estimates come mostly from observational studies, which may be biased because of difficulties in identifying and adjusting for confounders. In this paper, we examine the potential sources of bias in observational studies of influenza vaccine effectiveness in the elderly and we discuss available evidence regarding the efficacy and effectiveness of licensed influenza vaccines. Although several methodological criticisms among the available analyses on seasonal vaccines for elderly were identified, overall seasonal influenza vaccines showed relevant efficacy/effectiveness in reducing the risk of influenza and its complications in the elderly, considering different measure of outcome.