Loss of Vaccine-Induced Immunity to Varicella over Time

Active surveillance of a sentinel population of 350,000 persons was performed to determine whether the severity and incidence of breakthrough varicella increased with the time since vaccination. The annual rate of breakthrough disease significantly increased with the time since vaccination, from 1.6 cases per 1000 person-years within 1 year after vaccination to 9.0 at 5 years and 58.2 at 9 years. A second dose of varicella vaccine is now recommended. The annual rate of breakthrough varicella significantly increased with the time since vaccination, from 1.6 cases per 1000 person-years within 1 year after vaccination to 58.2 at 9 years. The implementation of a universal varicella vaccination program in the United States in 1995 has resulted in a substantial reduction in morbidity, mortality, and health care costs associated with the disease. 1 – 5 Despite this success, however, outbreaks of varicella continue to occur, mostly in highly vaccinated school communities. 6 – 8 Several studies of these school outbreaks have suggested that the time since vaccination may be associated with the risk of breakthrough varicella. 6 – 10 It has been hypothesized that exogenous reexposure to the virus may be needed to boost humoral and cellular immunity to varicella–zoster virus (VZV). 11 As the incidence of varicella . . .