Evolution of varicella surveillance--selected states, 2000-2010.

Varicella surveillance practices have evolved since varicella first became nationally notifiable in 1972 (1) (Table 1). Because national surveillance data were not adequate for monitoring the impact of varicella vaccine when it became available in the United States, active surveillance for varicella was established in sentinel sites in 1995 (1,2). With declines in varicella incidence after 1 dose of varicella vaccine was added to the routine childhood vaccination schedule in 1996 (3) and a second dose was recommended in 2006 (4), the number of cases of varicella in the active surveillance sites became insufficient to monitor further impact of vaccination. CDC evaluated varicella surveillance data reported via the National Notifiable Diseases Surveillance System (NNDSS) during 2000-2010 to determine whether these data might now be adequate for monitoring vaccination impact. By 2010, a total of 39 states required reporting of varicella cases, 38 states were conducting passive case-based surveillance, and 31 met CDC's ad hoc criteria for adequate and consistent reporting. Varicella incidence in the states that met these criteria declined 79% overall, from 43 per 100,000 population in 2000 to nine in 2010. While 1 dose of varicella vaccine was recommended, incidence declined 43% during 2000-2005, and after a second dose was added to the routine childhood schedule, incidence declined 72% during 2006-2010. State varicella surveillance data reported to CDC through NNDSS are now adequate for monitoring trends in varicella incidence, but continued strengthening of the surveillance system and participation of all states is needed.