Influenza Vaccination

E:pideniol. Infect. (1995), 115, 581-589 Copyright (© 1995 Cambridge University Press

581

Study of the effectiveness of influenza vaccination in the elderly in the epidemic of 1989-90 using a general practice database
D. M. FLEMING', J. M. WATSON2*, S. NICHOLAS2, G. E. SMITH2

AND A. V. SWAN2

'Birmningham Research Unit of the Royal College of General Practitioners, 54 Lordswood Road, Harborne, Birmingham B17 9DB.
2PHLS Comnnunicable Disease Surveillance Centre, 61 Colindale Avenue, London NW9 5EQ
(Accepted 24 July 1995)
SUMMARY The effectiveness of influenza vaccination in preventing serious illness and death was determined in an elderly population during the influenza epidemic of 1989-90. A retrospective cohort study was carried…show more content…
After adjustment for the effects of age, sex, underlying illness and number of consultations with the GP, the analysis showed that vaccination was significantly associated with a reduction in mortality. The best estimate of protection against death of influenza vaccination is thus 75 % (95 % confidence intervals: 21 to 92 %) for vaccination in the epidemic year and 22 % (95 % confidence intervals: -37 to 56 %) for vaccination in the previous year. Protection was also suggested when the definition of the outcome of interest was expanded to include respiratory illness in the epidemic period, but this was not statistically significant. Some of the deaths occurring in both the vaccinated and unvaccinated groups were likely to be due to causes unrelated to influenza and such mis-classification will bias estimates of efficacy against influenza related deaths. However this bias would tend to produce an under-estimate of protection and, despite this, the results suggest an overall protective effect of influenza vaccination, in those over 55 years of age in this population, against death. It is not possible to determine the precise causes of death in the patients involved in this study as this information was not included on the database. Conversely it seems that…show more content…
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