Varicella disease has declined dramatically in surveillance areas with moderate vaccine coverage. Continued implementation of existing vaccine policies should lead to further reductions of varicella disease in these communities and throughout the United States.

Context Limited data are available on the contagiousness of vaccinated varicella cases. Objectives To describe secondary attack rates within households according to disease history and vaccination status of the primary case and household contacts and to estimate varicella vaccine effectiveness. Design, Setting, and Patients Population-based, active varicella surveillance project in a community of approximately 320000 in Los Angeles County, California, during 1997 and 2001. Varicella cases were reported by child care centers, private and public schools, and health care clinicians and were investigated to collect demographic, clinical, medical, and vaccination data. Information on household contacts' age, varicella history, and vaccination status was collected.

No abstract

Clinical varicella reinfections may occur more commonly than previously thought. Additional studies of the predictive value of a positive varicella history and laboratory studies of reported reinfections are indicated to guide varicella vaccination policy.