The use of polysaccharide pneumococcal vaccination in elderly or high risk populations remains controversial. Evidence from less developed countries is the most persuasive in the absence of HIV, but in more developed countries the nine randomised controlled trials to date are inconclusive. They have now been the subject of some five meta-analyses^1–5 and to this can be added a recent meta-analysis of both the randomised controlled trials and observational studies.⁶ There has even been a review of the meta-analyses!⁷

The most recent review is helpful because it compares the trials and the observational studies using similar quality criteria and methods of pooling results. The strongest evidence is based on pneumococcal bacteraemia as the end point. Here studies of all types—case-control, cohort and randomised controlled trials—show consistent evidence of around 50% protection. However, it remains unclear whether this represents true protection or a suppression of bacteraemia without affecting the underlying disease (pneumonia). When it comes to pneumonia, the picture is much more confusing—and here we …