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Influenza vaccination in the elderly

Most of the deaths due to influenza occur among people aged over 60 years of age. It is in this group, and others with particular medical disorders (heart or lung disorders, diabetes, chronic renal insufficiency or chronic staphylococcal infections), that influenza vaccination is recommended. The question of how effective the vaccination policy is in elderly persons has been answered by a randomised controlled trial published recently in the Journal of the American Medical association [1].

The study was conducted in the winter of 1991-2 in southern Holland. Nearly 10,000 people not known to be belonging to a high-risk group in 15 practices were asked whether they wished to take part in the study and just under 2,000 accepted.

Randomised controlled trial

People were randomly allocated to active vaccine or control, which were given in double-blind conditions in weeks 44-46 (November 1-16). The active vaccine consisted of two Beijing strains, a Singapore and a Panama strain.

Participants gave blood samples before vaccination, three weeks later, and five months later for serological testing for increased antibody levels. The participants and their GPs also completed forms relating to any symptoms of influenza according to defined protocols.

The vaccination occurred before a peak of influenza incidence in Holland, during three weeks at the end of 1991.

Results

In the vaccinated population the rate of influenza or influenza-like illness was half that in the vaccinated population compared with the population given a placebo vaccination. For influenza confirmed both clinically and serologically, the relative risk was 0.42 (CI 0.23 to 0.74).

Using the more user-friendly numbers-needed-to-treat (NNT) method of calculating the results, of about two cases of influenza expected each winter in every 23 people aged over 60 years, one was prevented by influenza vaccination. Preventing one case of influenza for every 23 people treated, and preventing half the cases in elderly people is a very positive result, and one which should encourage the active pursuit of the policy of influenza vaccination.

Conclusion

With the JAMA paper is a very thoughtful editorial [2]. As well as commenting generally on the need for RCTs, and on the effectiveness of this RCT in particular, it reviews much up-to-date literature on the effectiveness of influenza vaccination. It refers to several studies in which substantial savings were demonstrated in direct medical costs during successive influenza seasons among elderly people who had been vaccinated.

The editorial delivers a simple message, based on the RCT and other evidence. "Influenza vaccination works, it's inexpensive, and it saves money".

References

  1. ME Govaert, CTMNC Thijs, N Masurei, MJW Sprenger, GJ Dinant, JA Knottnerus. The efficacy of influenza vaccination in elderly individuals. A randomized double-blind placebo-controlled trial. Journal of the American Medical Association 1994 272:1661-5.
  2. PA Patriarca. A randomised controlled trial of influenza vaccine in the elderly. Scientific scrutiny and ethical responsibility. Journal of the American Medical Association 1994 272:1700-1.



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