The Cochrane Library was systematically searched for meta-analyses regarding influenza vaccination of various populations, both healthy and sick. An effect in reducing the number of cases of influenza, influenza-like illness or complications to influenza was found in some studies, but, generally, the quality of the studies was low, and several studies lacked hard clinical endpoints. Data on adverse effects were scarce. More randomised controlled trials investigating the effects of influenza vaccination are warranted.