Younger age at vaccination may increase risk of varicella vaccine failure

J Infect Dis. 2002 Jul 1;186(1):102-5. doi: 10.1086/341089. Epub 2002 Jun 5.


To determine vaccine effectiveness (VE), a varicella outbreak in a highly vaccinated day-care center (DCC) population in Pennsylvania was investigated. In Pennsylvania, proof of immunity is required for children >or=12 months old for DCC enrollment. Questionnaires were administered to parents of children who had attended the DCC continuously during the study period (1 November 1999-9 April 2000) to determine history of varicella disease or vaccination and for information about any recent rash illnesses. VE was calculated for children >or=12 months old without a history of varicella. There were 41 cases of varicella among 131 attendees, with 14 cases (34%) among vaccinated children. VE was 79% against all varicella and 95% against moderate or severe varicella. Vaccination at <14 months was associated with an increased risk of breakthrough disease (relative risk, 3.0; 95% confidence interval, 0.9-9.9). Despite varicella vaccination coverage of 80%, a sizeable outbreak occurred. Early age at vaccination may increase the risk of vaccine failure.

MeSH terms

  • Age Factors
  • Chickenpox / epidemiology
  • Chickenpox / prevention & control*
  • Chickenpox Vaccine / administration & dosage*
  • Child
  • Child Day Care Centers
  • Child, Preschool
  • Disease Outbreaks
  • Female
  • Humans
  • Infant
  • Male
  • Risk Factors
  • Surveys and Questionnaires
  • United States / epidemiology
  • Vaccination*


  • Chickenpox Vaccine