I had an email this week from 67-year-old lady asking about flu vaccination. She’s had a phone call recently from her surgery asking her to attend for this. She asks if the “flu threat really worse this year or are the drug manufacturers up to their old tricks again!?”
Flu vaccination is generally promoted as a ‘no-brainer’ interventions by many in medicine. But how much evidence is there that it helps the elderly – the people some claim are most at risk and stand to gain the most from vaccination?
The effects of flu vaccination in the elderly was reviewed by researchers from the so-called ‘Cochrane Collaboration’ in 2010 [1]. The reviewers identified 75 studies, but only one of these was deemed especially relevant in that it was a ‘randomised controlled trial’. This study, apparently, yielded some evidence that vaccination helped protect against the flu, but it did not assess the impact of this on complications. This is important because one could argue that getting the flu is neither here nor there really. What is really important is whether this then leads to an enhanced risk of things like pneumonia and death (particularly important in the elderly).
The authors of the review concluded that “The available evidence is of poor quality and provides no guidance regarding the safety, efficacy or effectiveness for people aged 65 years or older.”
In 2008, the American Journal of Respiratory and Critical Care Medicine published a study that sought to assess the claim that flu vaccination helps stop old people dying [2]. Previous studies have found that if you look at an elderly population, those who have had the flu vaccination are about half as likely to die compared to those who remain unvaccinated. It’s obvious then: vaccination saves lives.
However, the ‘epidemiological’ studies tell us that vaccination is associated with reduced mortality, but they don’t tell us for sure that it’s the vaccination that is the protective factor.
One could argue, as the authors of this recent study did, that people who get flu vaccinations are also more health conscious (and perhaps they eat better, exercise more and smoke less) than those who eschew flu vaccination. Perhaps it is these or similar factors, not flu vaccination, that accounts for the reduced mortality in those who have been vaccinated?
To address this issue, these researchers assessed the mortality in about 350 vaccine recipients and 350 non-vaccinated individuals (controls) who had been hospitalised with pneumonia. The really clever twist to the design of this study was its timing: the study was done outside the flu season. Now, with no flu around to be protected from, any difference in mortality is unlikely to be due to flu vaccination.
What the researchers found was that those who had had the flu shot were (still) about half as likely to die compared to the non-vaccinated. The authors of this study suggest that the apparent mortality benefit in the elderly (as observed in epidemiological studies) is probably not due to the vaccine but, but a ‘healthy user’ effect.
I can’t know whether drug companies are up to their old tricks and over-hyping the need for flu vaccination. I also can’t know whether the lady who emailed me is likely to benefit from this intervention. The fact is the practice of flu vaccination in the elderly is not based on evidence, but an article of faith.
References:
1. Jefferson T, et al. Vaccines for prevent influenza in the elderly (review). The Cochrane Library 2010 (issue 2)
2. Dean T, et al. Mortality Reduction with Influenza Vaccine in Patients with Pneumonia Outside “Flu” Season – Pleiotropic Benefits or Residual Confounding? American Journal of Respiratory and Critical Care Medicine 2008;178:527-533
