A varicella outbreak in a school with high one-dose vaccination coverage, Beijing, China.
BACKGROUND
Varicella 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.


METHODS
A 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.


RESULTS
Of 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.


CONCLUSIONS
Single-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.
Beijing Center for Disease Control and Prevention, Beijing, PR China.
Li
L
Lu
Luodan
L
Suo
Juan
J
Li
Lijun
L
Zhai
Qingxiu
Q
Zheng
Xinghuo
X
Pang
Stephanie R
SR
Bialek
Chengbin
C
Wang
D002644:Chickenpox / Q000453:epidemiology* / Q000276:immunology / Q000821:virology; D019433:Chickenpox Vaccine / Q000008:administration & dosage* / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks / Q000517:prevention & control*; D005260:Female; D014645:Herpesvirus 3, Human / Q000276:immunology / Q000472:pathogenicity; D006801:Humans; D008297:Male; D012307:Risk Factors; D012574:Schools; D013334:Students / Q000706:statistics & numerical data; D013997:Time Factors; D014611:Vaccination
D019433:Chickenpox Vaccine