The Parental Strain of the Attenuated Virus (vOka) Used in the Varicella Vaccine Is Circulating in China: Implications for Vaccine Surveillance

Abstract

Varicella-zoster virus (VZV) is the etiological agent of both varicella (chickenpox) and herpes zoster (shingles). Primary infection with VZV causes varicella, which usually occurs in childhood. Reactivation of VZV in previously infected individuals results in a herpes zoster that occurs most commonly in the elderly. In 1974, a live-attenuated VZV strain was established and subsequently licensed for vaccination in Japan (1). Comparison of the complete DNA sequences of the Oka vaccine strain (vOka) and the parental Oka strain (pOka) revealed there were only 42 nucleotide substitutions along the whole 125-kbp viral genome, 15 of which were located in the major transactivator ORF62 region (2). The high sequence homology between vOka and pOka increases the difficulty of distinguishing vOka from clinical isolates with the pOka genotype. The pOka-like wild-type strain constitutes 20–30% of all VZV isolates in Japan (3). In contrast, it seems a rare genotype in other countries such as the U.S. and Australia (4,5). In this study we report a case of herpes zoster infected by the pOka-like wild-type strain in a Chinese woman. A 27-year-old woman who was 8 months pregnant presented to the First Affiliated Hospital of Anhui Medical University (Hefei, China) with vesicle skin lesions. The diagnosis of zoster was made mainly based on the history and features of the rash. The zoster rashes had developed on the right side of her abdomen, and she had no post-herpetic neuralgia. VZV was isolated in human embryonic lung fibroblasts from vesicle fluid taken from the patient on day 2 after the onset of zoster and was identified by immunocytochemistry with monoclonal antibodies to VZV glycoprotein E (Biodesign International ® , Saco, Maine, USA). This strain is hereafter designated as ZW strain. Serologic assay by fluorescent antibody to the membrane antigen (FAMA) test revealed a specific VZV IgG antibody titer of 1:8 in the serum colleted on day 2, and 1:256 in the second serum specimen obtained 16 days after the onset of symptoms. Viral DNA was extracted from the fluid of the rash vesicles