Comparison of humoral immune responses to trivalent influenza split vaccine in young, middle-aged and elderly people.

A total of 296 volunteers in five different groups were immunized with one dose of the commercial 1991-1992 trivalent split influenza vaccine formulation A/Singapore/6/86 (H1N1), A/Beijing/353/89 (H3N2) and B/Yamagata/16/88. The groups differed in age (young adults, middle-aged and elderly) and history of previous vaccination. Antibodies were determined in pre- and postvaccination sera by haemagglutination inhibition assay and the results were evaluated as geometric mean titre, mean fold antibody increase, protection and response rates. No significant age-related differences among the protection rates were found. The proportion of vaccinees with antibodies > or = 40 ranged between 70 and 95%. Compared with the H3N2 and B components the antibody response to the H1N1-component was low. Residents of a nursing home fully vaccinated the previous year developed 7.6-8.4-fold antibody increases and showed 96-100% protection rates.