Seasonal influenza vaccination of the elderly

The elderly are at increased risk of the complications of seasonal influenza. Annual vaccination is therefore recommended. However, two systematic reviews published by the Cochrane collaboration have highlighted a number of outstanding issues. This article examines whether annual influenza vaccination of the elderly and their regular contacts is still supported by the available scientific evidence. The randomised trials included in one of the Cochrane reviews suggest that influenza vaccination reduces the incidence of flu-like syndromes and laboratory-confirmed influenza in the elderly. There are no robust randomised trials specifically designed to assess whether vaccination of the elderly prevents influenza complications. Two case-control studies showed a statistical correlation between vaccination and a lower risk of death from influenza complications. Cohort studies have also shown that complications are less frequent when the vaccine strains correspond to circulating strains. Because of a patient selection bias, non-randomised studies seem to overestimate the efficacy of vaccination. Three randomised trials showed that vaccination of care home staff reduced mortality among elderly residents during seasonal flu epidemics. No such effect was observed in another trial, possibly because a large proportion (32%) of staff in the control institutions had also been vaccinated. In practice, influenza vaccination of the elderly with risk factors for complications is justified, especially for care home residents, their regular contacts and healthcare workers. Seasonal flu vaccination of healthy people over 65 provides limited benefit but its harm-benefit balance remains favourable. More studies of routine influenza vaccination of the elderly are needed.