Effectiveness of influenza vaccination in the elderly in a community in Italy

Objectives: Assess the effectiveness of influenza vaccination in reducing h ospitalization due to pneumonia and influenza among elderly subjects in a c ommunity in central Italy. Estimate the hospitalization fraction preventabl e by extending the vaccination program. Methods: Case-control study. Cases were subjects aged 65+ at hospital admission (1 December 1994-31 March 1995 ). For each case two population controls were randomly chosen, matched by s ex, age and residence. Variables of interest were recorded through a postal questionnaire and telephone interview. A matched-set analysis was carried out adjusting for concomitant chronic diseases, education, type of home hea ting, and smoking habits. The preventable fraction of hospitalization was c omputed through the application of the attributable risk estimate. The sett ing was 33 municipalities in central Italy including 169,370 residents aged 65 years or more. Results: Two hundred and seventy-five cases 550 controls were analyzed. Influenza vaccination was effective in preventing 33% of ho spitalization due to pneumonia/influenza. The fraction of hospital admissio ns preventable by extending the vaccination was 17%. When the analysis was limited to self-respondents to the questionnaire (excluding next-of-kin) an d to pneumonia/influenza as primary discharge diagnosis, protection from ho spitalization by vaccination almost reached 50%, a better result in compari son with most case-control studies. Conclusions: Influenza vaccination was shown to be successful in reducing hospital admissions due to pneumonia and influenza. A large number of hospitalizations could be reduced extending t he vaccination campaign.