Reduction in hospital admissions for pneumonia in non-institutionalised elderly people as a result of influenza vaccination: a case-control study in Spain

Objective-To estimate the effectiveness of influenza vaccine in preventing hospital admission for pneumonia in non-institutionalised elderly people. Design-This was a case-control study. Setting-All three public hospitals in the Castellon area of Spain. Participants-Cases were people aged 65 or more not living in an institution who were admitted to hospital for pneumonia between November 15, 1994 and March 31, 1995. Each case was matched with two sex matched control subjects aged 65 years or older admitted to hospital in the same week for acute abdominal surgical conditions or trauma. The sampling of incident cases was consecutive. Eighty three cases and 166 controls were identified and included in the study. Measurements-Trained interviewers completed a questionnaire for each subject on the vaccination status, smoking habits, previous diseases, health care use, social contacts, family background, the vaccination status of the family carer, home characteristics, and socioeconomic status. Results-The adjusted odds ratio of the influenza vaccination preventing admission to hospital for pneumonia was 0.21 (95% confidence interval 0.09, 0.55). The variables which best explained the risk of being a case were age, intensity of social contacts, health care use, previous diseases, and the existence of a vaccinated family carer. Conclusions-Influenza vaccination reduced significantly hospital admissions for pneumonia in non-institutionalised elderly people.