Inactivated influenza vaccines in the elderly-are you sure?

摘要

In 2005 and 2006 we published Cochrane Reviews of the effects of influenza vaccines in people aged 65 years or older, and an overview of evidence from systematic reviews of comparative studies of all age groups.3 The review of elderly people highlighted the thinness of the randomised evidence for this age group and the unreliable nature of evidence from cohort studies, especially large retrospective studies with data linkage. These cohorts contributed the largest proportion of evidence. We commented on the implausibility of our findings: eg, in individuals living in the community, vaccines were apparently effective for the prevention of non-specific outcomes such as death from all causes, but not for the prevention of influenza or death caused by pneumonia and influenza (figure). We concluded that the most probable explanation for such contradictory findings was selection bias, which occurred when not-so-frail elderly people were more likely to be vaccinated than their infirm peers, thus affecting the outcome