Influenza vaccines: Poor evidence for effectiveness in elderly

Adults aged 65 and over are some of the most vulnerable during influenza season and a priority for vaccination programmes. However, very few systematic reviews of the effectiveness of vaccines in this group have ever been carried out.

The researchers conducted a thorough search of studies based on previous vaccine trials. Randomised controlled trials (RCTs) are often considered the "gold standard," but of the 75 studies included in their review, the researchers were only able to identify one recent RCT with "real" outcomes. In other words, this was the only RCT that used influenza cases as an outcome, as opposed to surrogate outcomes such as measurements of influenza antibodies in the blood. All the other studies included in the review were deemed of low quality and open to bias.

Limited reliable evidence from the studies suggests that the effectiveness of influenza vaccines is modest at best. "Our estimates are consistently below those usually quoted by economists and in decision making," says lead researcher Tom Jefferson of the Cochrane Collaboration in Rome, Italy. "But until we have all available evidence, it is hard to reach any clear conclusions about the effectiveness of influenza vaccines in older people."

"As the evidence is so scarce at the moment, we should be looking at other strategies to complement vaccinations. Some of these are very simple things like personal hygiene, and adequate food and water," says Jefferson. "Meanwhile, we need to undertake a high quality, publicly funded trial that runs over several seasons to try to resolve some of the uncertainties we're currently facing."

Jefferson is also one of the authors of a second review publishing this week, which focuses on the efficacy of influenza vaccinations in healthcare workers who work with the elderly. The results are also inconclusive, with each of the four trials included in the review being of inadequate quality and reaching implausible conclusions. The researchers were unable to draw any conclusions about whether vaccinating healthcare workers helps to prevent influenza symptoms and death in people aged over 60.