Failure of influenza vaccination in the aged.

A cohort of 127 nursing home residents aged 60-98 years were vaccinated during the winter of 1985-86 with the A-Chile 1/83 (C), A-Philippines 2/82 (P), and B-USSR (B) commercial influenza vaccines. Before vaccination 40%, 23%, and 69% were susceptible to influenza Ac, Ap, and B, respectively [hemagglutinin inhibition (H.I.) titer less than 1:40]. One month following initial vaccination, 32 patients [25%] remained unprotected against two or all three vaccine strains. These patients were revaccinated with the same influenza vaccine and followed up. At five months 11%, 19%, and 23% of the initial cohort were still unprotected against Ac, Ap, and B strains, respectively. We conclude that two conventional influenza vaccines administered one month apart leave unprotected 30% of healthy elderly people who are initial influenza vaccine failures.