Smoking and influenza in the elderly: a sero-epidemiological study.

Two blood samples were taken at an interval of five years in a continuing epidemiological study of a rural population with an age range of 40-64 years at commencement. Paired sera of 111 light smokers and their non-smoker controls, matched for age and sex, and of 68 heavy smokers and their respective controls were tested for haemagglutination inhibiting antibodies against four different influenza strains. Antibodies were detected in the baseline specimens more frequently and in higher titres among the smokers than among the controls. Significant rises in titre between the baseline specimens and the follow-up specimens occurred slightly more frequently among the smokers.