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As varicella vaccine coverage continues to increase (now approaching 90% in the U.S.), fewer unvaccinated children have natural immunity. As a result, a reported history of varicella may no longer predict serologic immunity. Between 2004 and 2006, investigators in Philadelphia assessed the validity of self-reported and parent-reported varicella history in 1476 unvaccinated children and young adults (age range, 1–29 years) from seven community-based sites by comparing histories with varicella-zoster virus immunoglobulin G serological results.
Only 4% of children aged 1 to 4 years were seropositive. The positive predictive value (PPV) of a reported history of varicella for seropositivity increased with age: 1–4 years (born in 2000–2004), 43%; …