Transmission of Varicella Vaccine Virus, Japan

To the Editor: Varicella-zoster virus (VZV), a human herpesvirus, is the causative agent of varicella (chickenpox) and herpes zoster (shingles). Worldwide, children are routinely vaccinated with a live attenuated varicella vaccine containing the Oka vaccine (vOka) strain of VZV, originally developed in Japan (1–3). Although the risk for secondary transmission of the vOka strain from immunocompromised vaccinees to susceptible persons is relatively high, the risk for transmission from immunocompetent vaccinees is low (1). We report secondary transmission of the vOka strain from an immunocompetent girl with a history of varicella vaccination to her healthy susceptible brother. Herpes zoster developed in a healthy 3-year-old girl 2 years after she had received the varicella vaccine (lot VZ040; Biken, Osaka, Japan). She received oral acyclovir treatment and fully recovered by day 19 after herpes zoster onset. On the same day that the girl recovered, her immunocompetent 2-year-old brother was found to have fever and a rash consisting of 10–20 papulovesicles; mild varicella was diagnosed. The boy had no known history of contact with persons infected with varicella or with persons who administered the varicella vaccine. After receiving oral acyclovir treatment, the boy recovered without systemic complications. On day 19 after the girl’s onset of herpes zoster, an enzyme immunoassay (Denka Seiken, Tokyo, Japan) confirmed the presence of VZV-specific immunoglobulin (Ig) G (titer 48.9, well above the detection limit of 2.0) but not IgM. The boy showed seroconversion of VZV-specific IgG from a titer of