This study evaluates the remaining effect of influenza vaccines received in the 5 prior seasons. During 7 influenza seasons 8933 patients were enrolled and 47% were confirmed for influenza. As compared to unvaccinated individuals in the current and 5 prior seasons, vaccination was protective when the last dose had been received in the current season (40%; 95%CI, 32-47), and one (42%; 95%CI, 27-54), 2-3 (35%; 95%CI, 16-49) or 4-5 seasons before (31%; 95%CI, 4-51). This effect lasted less in the elderly and chronic patients. On average, several recent prior doses were as protective as current season vaccination.