Epidemiology of Varicella During the 2-Dose Varicella Vaccination Program - United States, 2005-2014.

Before availability of varicella vaccine in the United States, an estimated 4 million varicella cases, 11,000-13,500 varicella-related hospitalizations, and 100-150 varicella-related deaths occurred annually. The varicella vaccination program was implemented in the United States in 1996 as a 1-dose routine childhood program. Based on data from two varicella active surveillance sites, the varicella vaccination program led to 90% decline in incidence over the next decade (1). However, because of continued varicella outbreaks, a routine 2-dose schedule (at ages 12-15 months and 4-6 years) was recommended and has been in place since 2006 (2). The declines in incidence (1,3-6) made it feasible for states to implement varicella case-based surveillance and to report varicella data to CDC through the National Notifiable Diseases Surveillance System (NNDSS). State data have become the primary source for monitoring trends in varicella incidence nationally (7). Using NNDSS data, CDC previously reported nationwide declines in varicella incidence of 72% from the end of the 1-dose to the early years of the 2-dose varicella vaccination program (2006-2010) (7). This report updates varicella incidence trends to include the most recent years in the 2-dose varicella vaccination program. Between the period 2005-2006 (before the 2-dose recommendation) and 2013-2014, overall varicella incidence declined 84.6%, with the largest declines reported in children aged 5-9 years (89.3%) and 10-14 years (84.8%). The availability of varicella-specific data varied over time. During the last 2 years examined (2013 and 2014), completeness of reporting of two critical variables monitored by CDC, vaccination status (receipt of at least 1 dose of varicella vaccine) of cases and severity of disease based on number of lesions, were 54.2% and 39.1%, respectively. State and local health departments, in collaboration with CDC, should continue working to improve reporting of cases and completeness of critical varicella-specific variables to better monitor impact of the varicella vaccination program.