Role of influenza vaccination in the elderly during an epidemic of A/H1N1 virus in 1988-1989: clinical and serological data.

During a winter epidemic of A/H1N1 influenza virus, we evaluated the protection conferred by vaccination of 285 residents of a nursing home. Fifteen of 204 members of the nursing staff were also vaccinated. Serological determinations were performed before and after vaccination using radial hemolysis (RH) and neuraminidase inhibition (NI) tests. In the outbreak period, only one influenza case was noted in the vaccinated elderly and none among the vaccinated nursing staff. On the other hand, 38 cases (20%) occurred in the unvaccinated hospital personnel. Twenty-one percent of the elderly people exhibited seroconversion to the vaccinal strain by RH and NI while 27 and 20% of the vaccinated nursing staff seroconverted by the same tests, respectively. Thus, the clinical protection conferred by influenza vaccination was excellent and much greater than expected from serological results.