Varicella Disease among Vaccinated Persons: Clinical and Epidemiological Characteristics, 1997–2005

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Abstract
Approximately 1 in every 5 children who receives 1 dose of varicella vaccine may develop varicella disease, also known as breakthrough disease, if exposed to varicella-zoster virus. Currently, in communities with high vaccination coverage, varicella cases mostly occur in vaccinated individuals. We report on the first populationbased description of the clinical and epidemiological characteristics of varicella in populations with increasing vaccine coverage between 1997 and 2005. In vaccinated children 1–14 years of age, varicella was most often mild and modified; the atypical disease presentation may result in diagnostic challenges to health care providers. However, despite the generally mild nature of these cases, ∼25% caused >50 lesions, and some resulted in serious complications similar to those occurring in unvaccinated individuals. Continued surveillance of the risk and characteristics of breakthrough disease will be needed, to monitor the effect of the new 2-dose vaccine recommendation for children.