Varicella disease after introduction of varicella vaccine in the United States, 1995-2000.

CONTEXT Before licensure of varicella vaccine in 1995, varicella was a universal childhood disease in the United States, causing 4 million cases, 11,000 hospitalizations, and 100 deaths every year. OBJECTIVE To examine population-based disease surveillance data in 3 communities to document the impact of the varicella vaccination program. DESIGN, SETTING, AND SUBJECTS Active surveillance for varicella conducted among the populations of Antelope Valley, Calif; Travis County, Tex; and West Philadelphia, Pa; from January 1, 1995, to December 31, 2000. Reporting sites included child care centers, schools, universities, physicians, public health clinics, hospitals, emergency departments, and households. MAIN OUTCOME MEASURES Trends in number and rate of varicella cases and hospitalizations; varicella vaccine coverage. RESULTS From 1995 through 1998, in each surveillance area, the number of verified varicella cases varied from year to year with marked springtime seasonality. In 1999, the number and rates of varicella cases and hospitalizations declined markedly. From 1995 through 2000, in Antelope Valley, Travis County, and West Philadelphia, varicella cases declined 71%, 84%, and 79%, respectively. Cases declined to the greatest extent among children aged 1 to 4 years, but cases declined in all age groups, including infants and adults. In the combined 3 surveillance areas, hospitalizations due to varicella declined from a range of 2.7 to 4.2 per 100,000 population in 1995 through 1998 to 0.6 and 1.5 per 100,000 population in 1999 and 2000, respectively (P =.15). By 2000, vaccine coverage among children aged 19 to 35 months was 82.1%, 73.6%, and 83.8% in Los Angeles County, Texas, and Philadelphia County, respectively. CONCLUSIONS 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.