Influenza mortality and hospital admissions for influenza, pneumonia, emphysema and bronchitis during the influenza epidemic 1989-90 : case-control study of risk-factors and effectiveness of influenza vaccine

General practitioners' records for 315 subjects whose primary or contributory cause of death was influenza between November 4, 1989 and February 23, 1990, and 777 controls, matched for age, sex, and area of residence, who died a year after the epidemic were reviewed. Information was collected on demography, usual place of residence (institutional or non institutional), and existence of chronic illness. Conditional logistic regression analysis for matched case-control studies showed that influenza vaccination reduced mortality by 41% (95% Cl 13 - 60%) for all subjects. Among subjects who received the vaccine for the first time in 1989, vaccination reduced mortality by 9% (95% CI 0 - 50); however among those who had also been vaccinated previously, mortality was reduced by 75% (95% CI 31 - 91). There were no significant differences in the effect of vaccine between subjects who lived in institutions and in the community (p=0.16), or between subjects with high-risk medical conditions and those without (p=0.76). Influenza vaccine is effective in reducing mortality from influenza, and effectiveness seems to be greater after repeated annual vaccination than after first time administration.;Vaccine up-take among cases and controls was only 21.5% but 77% of individuals had an indication for vaccination as recommended by the DoH. There was no significant difference in the proportion of patients in each of the DoH high-risk groups who were vaccinated (x2 = 7, p = 0.07). Multiple logistic regression showed that three factors significantly affected the likelihood of immunisation in 1989 - 90; more frequent consultations with GP during the 12 months before death (OR 1.04, CI 1.03 - 1.04), living in residential care (OR, 1.45, CI 1.17 - 1.79), and 'previous' vaccination (between 1985 - 88) (OR 7.61, CI 6.06 - 9.56).;Of the 315 fatal influenza cases identified 299 (94.9%) were 65 years or older and 263 (83.5%) had an indication for vaccination.