An elementary school outbreak of varicella attributed to vaccine failure: Policy implications

Brian R. Lee, Shelly L. Feaver, Claudia A. Miller, Craig W. Hedberg, Kristen R. Ehresmann

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Background. Since licensure in the United States, studies have shown that varicella vaccine's overall effectiveness ranges from 44% to 100%, with substantial protection against moderate and severe varicella; however, breakthrough illness has been documented in up to 56% of vaccinated individuals. Methods. A varicella outbreak occurred in a Minnesota school with 319 students. Phone surveys were conducted with students' parents. Information was collected on students who had recent varicella infections, including onset date, rash characteristics, duration, and underlying medical conditions. Results. Fifty-four cases occurred after a primary breakthrough case. Twenty-nine (53%) students had been vaccinated. Unvaccinated students had an increased risk of moderate varicella, compared with vaccinated students (relative risk [RR], 4.4 [95% confidence interval {CI}, 2.2-9.1]; P < .001). The vaccine was 56% effective at preventing any varicella and 90% effective against moderate illness. Students vaccinated ≥5 years before the outbreak had a greater risk of breakthrough varicella than did those vaccinated within ≤4 years (RR, 2.6 [95% CI, 1.3-5.4]; P < .01). Conclusions. Vaccinated students presented with milder varicella symptoms than did unvaccinated students. Individuals with breakthrough illness can be highly infectious. Time since varicella vaccination was associated with illness. Despite 29 breakthrough cases, the varicella vaccine conferred a high degree of protection against moderate illness.

Original languageEnglish (US)
Pages (from-to)477-483
Number of pages7
JournalJournal of Infectious Diseases
Issue number3
StatePublished - Aug 1 2004

Bibliographical note

Funding Information:
Received 6 January 2004; accepted 2 February 2004; electronically published 29 June 2004. Financial support: Centers for Disease Control and Prevention, National Immunization Program. The contents of the present study are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention. a Present affiliation: Acute Disease Investigation and Control Section, Minnesota Department of Health, Minneapolis. Reprints or correspondence: Brian Lee, Acute Disease Investigation and Control Section, Minnesota Dept. of Health, 717 Delaware St. SE, Minneapolis, MN 55414 (


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