Postexposure effectiveness of varicella vaccine

Objective. 1) To describe the postexposure effectiveness of varicella vacci ne in a homeless shelter; and 2) to demonstrate an effective public health intervention and its implications. Design. A prospective observational study. Setting. A women and children's shelter in Philadelphia with 2 cases of var icella before intervention. Outcome Measures. Varicella in vaccinated and unvaccinated shelter resident s; vaccine effectiveness for prevention of varicella when administered afte r exposure among children <13 years of age. Results. Sixty-seven shelter residents received varicella vaccine after exp osure, including 42 children <13 years of age. One child who was unvaccinat ed developed varicella, but no vaccinated child developed typical disease. Vaccine effectiveness was 95.2% (95% CI, 81.6%-98.8%) for prevention of any disease and 100% for prevention of moderate or severe disease among the ch ildren <13 years of age. Conclusion. When used within 36 hours after exposure to varicella in a sett ing where close contact occurred, varicella vaccine was highly effective in preventing further disease. This study provides support for the recent rec ommendation by the Advisory Committee on Immunization Practices to administ er varicella vaccine after exposure: this practice should minimize the numb er of moderate or severe cases of disease and prevent prolonged outbreaks.