Evaluation of the impact of an HMO's varicella vaccination program on incidence of varicella.

The impact of a varicella vaccination program on disease in a large HMO population during 1996-1999 was assessed by multiple cross-sectional analyses of automated database records of vaccinations and varicella diagnoses for children (0-18 years). The cumulative proportion of the population vaccinated reached 73% among 2-year-olds, and 22% overall. An overall 49.7% reduction in varicella incidence was estimated to be attributable to an 18.5% point increase in the proportion of the population vaccinated.