A varicella outbreak in a school with high one-dose vaccination coverage, Beijing, China |
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Authors: | Lu Li Suo Luodan Li Juan Zhai Lijun Zheng Qingxiu Pang Xinghuo Bialek Stephanie R Wang Chengbin |
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Institution: | Beijing Center for Disease Control and Prevention, Beijing, PR China. |
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Abstract: | BackgroundVaricella vaccine is available in the private sector in China, with a single dose currently recommended for children aged ≥12 months. We investigated a varicella outbreak in a school in Beijing with high varicella vaccination coverage to describe the outbreak, examine risk factors for vaccine failure, and calculate vaccine effectiveness.MethodsA varicella case was defined as an acute generalized maculopapular rash without other apparent cause in a student without prior varicella attending the elementary school during August 30–December 28, 2010. Varicella among vaccinated students (breakthrough varicella) was defined as varicella occurring >42 days after vaccination. Students’ vaccination status was verified with immunization records and clinical presentations were collected from health care practitioners.ResultsOf the 951 students, 934 (98%) had no prior varicella history. Among these students, 916 had received 1 dose of varicella vaccine and 2 had received 2 doses (98% vaccination coverage) before the outbreak. A total of 87 cases occurred during the outbreak; most had breakthrough varicella (86/87, 99%) and mild disease (83/87, 95%). Age at vaccination (<15 months vs. ≥15 months) and time since vaccination before outbreak (<5 years vs. ≥5 years) were not associated with development of breakthrough varicella. Single-dose varicella vaccination was 89% effective in preventing any varicella and 99% in preventing moderate/severe varicella.ConclusionSingle-dose varicella vaccination is highly effective in reducing varicella incidence and mitigating disease severity, but not high enough to prevent outbreak. A two-dose program might help to prevent varicella outbreaks in Beijing. |
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Keywords: | Varicella outbreak Varicella vaccine effectiveness |
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