Outbreaks of influenza in nursing homes still occur, even when a large port
ion of residents have been inoculated with inactivated vaccine. Data were c
ollected in 1991-1992 from 83 eligible skilled nursing homes located in sou
thern Lower Michigan to determine the effectiveness of inactivated influenz
a vaccine in preventing influenza-like illness and influenza-associated pne
umonia, Surveillance was conducted to identify the occurrence of influenza
in the homes and, at the end of the season, specific data were gathered on
all residents of homes with influenza activity. Age- and sex-adjusted estim
ates of vaccine effectiveness were calculated using Cox proportional hazard
s models for each nursing home. Estimates were pooled using precision-based
weights calculated from data for each home. Vaccine was found to be 33% ef
fective in preventing total respiratory illness (influenza-like illness and
clinically diagnosed pneumonia). In prevention of pneumonia alone, Vaccine
was 43% effective. The estimate for prevention of pneumonia rose to 55% if
the period under consideration was limited to the time of peak influenza a
ctivity. Given the number of eligible homes and the cohort methodology used
, the results support continuation of current policy, encouraging use of va
ccine in all nursing home residents.