Impact of Vaccination on the Epidemiology of Varicella: 1995

abstract BACKGROUND: When varicella vaccine was licensed in the UnitedStates in 1995, there were concerns that childhood vaccination mightincrease the number of adolescents susceptible to varicella and shiftdisease toward older age groups where it can be more severe.METHODS: We conducted a series of 5 cross-sectional studies in 1994to 1995 (prevaccine), 2000, 2003, 2006, and 2009 in Kaiser Permanenteof Northern California to assess changes in varicella epidemiology inchildrenandadolescents,aswellaschangesinvaricellahospitalizationinpeopleofallages.Foreachstudy,informationonvaricellahistoryandvaricella occurrence during the past year was obtained by telephonesurvey from a sample of ∼8000 members 5 to 19 years old; varicellahospitalization rates were calculated for the entire membership.RESULTS: Between 1995 and 2009, the overall incidence of varicella in5- to 19-year-olds decreased from 25.8 to 1.3 per 1000 person-years,a ∼90% to 95% decline in the various age categories (5–9, 10–14,and 15–19 years of age). The proportion of varicella-susceptiblechildren and adolescents also decreased in all age groups, includingin 15- to19-year-olds (from15.6%in1995 to7.6% in 2009).From1994 to2009, age-adjusted varicella hospitalization rates in the generalmember population decreased from 2.13 to 0.25 per 100000, a ∼90%decline.CONCLUSIONS: In the 15 years after the introduction of varicella vac-cine, a major reduction in varicella incidence and hospitalization wasobserved with no evidence of a shift in the burden of varicella to olderage groups. Pediatrics 2014;134:24–30