Influenza A/Philippines/2/82 outbreak in a nursing home: limitations of influenza vaccination in the aged.

The failure of the 1982-1983 influenza vaccine to protect elderly NHCU residents from clinical infection with influenza A/Philippines/2/82 resulted primarily from antigenic drift of the epidemic strain, inasmuch as the attack rates in the vaccinated and nonvaccinated patients were not significantly different. This experience supports the decision to replace A/Bangkok/1/79 with A/Philippines/2/82 virus antigen in the 1983-1984 influenza vaccine.