Abstract: ObjectiveTo analyze the gene characteristics of varicella-zoster virus (VZV) that caused an outbreak of chicken-pox in a primary school in Shanghai in 2007. MethodsThe virus was isolated in vesicular fluid collected from 5 patients by using MRC-5 cells and identified by standard serum for VZV. PCR-RFLP and nucleotide sequencing were performed to characterize the gene of isolated virus. ResultsThe virus that can cause cytopathic effect (CPE) of MRC-5 cells was isolated from 5 vesicular fluid samples and identified as VZV by the neutralization test with standard serum for VZV. PCR-RFLP and sequencing performed on fragment ORF22, 38, 54, 62 and 68 of VZV genome showed that all the isolated VZV were wild strains of genotype J (BglⅠ+，PstⅠ+，SmaⅠ+). VZV-MSP or VZV-BC-like genetic mutation in antigenic determinant 3B3 of glycoprotein E was not found in these VZV isolates. ConclusionThis outbreak of chicken-pox was caused by wild strain of VZV (genotype J). Among the patients, 41.1% had received varicella vaccine. Failure of initial immunization or decrease of antibody level might account for this chicken-pox outbreak. So it is necessary to conduct further study on the gene characteristics of VZV and varicella vaccine vaccination strategy.