Efficacy of influenza vaccine in the elderly in welfare nursing homes: reduction in risks of mortality and morbidity during an influenza A (H3N2) epidemic.

The effect of influenza vaccination on the occurrence and severity of influenza virus infection in a population residing in nursing homes for the elderly was studied during an influenza A (H3N2) epidemic in Japan. Of 22,462 individuals living in 301 welfare nursing homes, 10,739 received either one dose (2027 subjects) or two doses (8712 subjects) of inactivated, subunit trivalent influenza vaccine. During the period Nov. 1998 to March 1999, there were 950 cases of influenza infection diagnosed clinically, with virus isolation or serology. There were statistically significantly fewer cases of influenza, hospital admissions due to severe infection and deaths due to influenza in the vaccinated cohort (256 cases, 32 hospital admissions, 1 death) than in the unvaccinated controls (694 cases, 150 hospital admissions, 5 deaths; reduction rates 59.8%, 76.9% and 79.1% respectively). Vaccination was almost equally effective in those who received one dose of vaccine and those who received two doses. No serious adverse reactions to vaccination were recorded. Thus influenza vaccination is safe and effective in this population, and should be an integral part of the routine care of persons aged > or =65 years residing in nursing homes.