Increasing Evidence of Immunity to Varicella Among Children in Massachusetts, 1999–2003

BackgroundExperiences with vaccine-preventable diseases have demonstrated the success of school-entry requirements in increasing vaccination coverage and decreasing disease incidence. This study examines the effect of early implementation of daycare and school-entry requirements for varicella vaccination on recorded varicella immunity of preschool and school-aged children in Massachusetts.MethodsImmunization surveys were conducted in licensed child care centers and schools with kindergarten and/or 7th grades. Evidence of immunity to varicella was defined as having physician verified records of varicella vaccination or disease history from the 1999–2000 through 2003–2004 school years.ResultsDuring the 5-year study period, physician-certified reliable history of varicella disease decreased in each grade level while vaccination coverage increased. The increase in the number of children in each grade level receiving varicella vaccine led to an increase in the overall percentage of children with evidence of immunity to varicella: 85% to 97% for children aged 2 years or more in child care, 93% to 98% for children in kindergarten, and 88% to 92% for children in 7th grade.ConclusionsThe implementation of daycare and school-entry requirements for varicella vaccination within 4 years of the start of the varicella vaccination program in Massachusetts was associated with high levels of vaccination coverage in the cohorts of children targeted by the requirements. Although evidence of immunity from varicella disease decreased during the study period, the increase in varicella vaccination coverage compensated for the decline in disease history, resulting in a higher proportion of young children with evidence of immunity to varicella.