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

ABSTRACT

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.