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Influenza vaccination

Search and Results
Adverse effects
Comment


The end of the influenza season seems timely for the publication of an authoritative review of effectiveness of vaccines, ion-channel inhibitor antivirals and neuraminidase inhibitor antivirals [1], and to begin to plan for next Winter using some evidence. The review concatenates several Cochrane reviews, adds an economic evaluation and a definitive discussion of the problems of trial assessment in influenza. It concentrated on healthy adults aged 14 to 60 years, specifically avoiding vaccination in the elderly for which there is only one RCT ( Bandolier 11 ). A review of influenza vaccines in the elderly was published some years ago [2].

Search and Results


The search was typically thorough. The major outcome from the economic evaluation was that in healthy adults inactivated vaccines appear to be the best buy, if needed.

There were 14 comparisons evaluating inactivated influenza vaccines against placebo or non influenza vaccine in healthy adults. The outcome was clinically defined influenza cases. With influenza vaccine 1034/5953 people (17%) developed influenza, compared with 791/2798 people (28%) given control. Studies covered a range of influenza infection rates, and five individually showed vaccine statistically better than control. The mean reduction in influenza cases was by 29% (95% confidence interval 12 to 42%). It was somewhat higher when vaccines matched the circulating strain. The number needed to treat was 9.2 (7.8 to 11.1). This means that for every nine people given influenza vaccine, one avoided having influenza who would have had it if they had not been vaccinated.

Adverse effects


Local effects were reported by 69% of people given influenza vaccine. Some parenteral adverse effects were experienced by 30% of people given influenza vaccine, but no individual symptom was significantly commoner than control. Many could be attributed to influenza-like illnesses.

Comment


Bandolier will be more forceful with older relatives next winter. A 1 in 9 chance of avoiding influenza, with its possibly disastrous effects, is worth it if the downside is some local discomfort. Many older relatives complain about minor 'flu-like' illness after vaccination. We can tell them that it is not the vaccine. In older people from one trial the NNT was 23. For those who have to deliver healthcare to the elderly, this is essential reading. ImpAct would like to hear from groups showing how to deliver high vaccination rates.

Reference:

  1. V Demicheli, T Jefferson, D Rivetti, J Deeks. Prevention and treatment of influenza in health adults. Vaccine 2000 18: 957-1030.
  2. PA Gross et al. The efficacy of influenza vaccines in elderly people: a meta-analysis and review of the literature. Annals of Internal Medicine 1995 123: 518-527.
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