Varicella in infants after implementation of the US varicella vaccination program.

OBJECTIVE To describe varicella disease in infants since implementation of the varicella vaccination program in the United States. PATIENTS AND METHODS From 1995 to 2008, demographic, clinical, and epidemiologic data on cases of varicella in infants were collected prospectively through a community-based active surveillance project. We examined disease patterns for infants in 2 age groups: 0 to 5 and 6 to 11 months. RESULTS Infant varicella disease incidence declined 89.7% from 1995 to 2008. Infants aged 0 to 5 months had milder clinical disease than those aged 6 to 11 months: ≥50 lesions, 49% vs 58% (P = .038); fever (body temperature > 38°C), 12% vs 21% (P = .014); and varicella-related complications, 6% vs 14% (P = .009), respectively. Age was an independent predictor of the occurrence of complications. CONCLUSIONS The varicella vaccination program has resulted in substantial indirect benefits for infants, who are not eligible for vaccination. Presence of maternal varicella-zoster virus antibodies might explain attenuated disease in very young infants likely born to mothers with history of varicella. Although varicella disease incidence has declined, exposure to varicella-zoster virus continues to occur. Improving varicella vaccination coverage in all age groups will further reduce the risk of varicella exposure and protect those not eligible for varicella vaccination.