Each winter, most influenza deaths occur among seniors (although they were spared during the 2009 pandemic period). For nearly a decade, there has been a controversy brewing about the benefits of vaccinating seniors against influenza. The policy of vaccinating seniors was put in place in the 1960s in USA and other countries without much in the way of clinical trials demonstrating benefits, and the question was already raised at that time whether seniors could actually mount a protective response.1 More recently national analysis of influenza mortality time trends in several countries fueled this concern, as these studies saw no decline in flu-related deaths as vaccine coverage rose fourfold in seniors.2

This observation seemed to be in disagreement with the large body of evidence from observational studies that consistently reported a halving in total winter deaths (all cause mortality) in vaccinated seniors.3 4 But the paradox was there – how …