Long-term Effectiveness of the Live Attenuated Herpes Zoster Vaccine

This is a multicenter retrospective cohort study to evaluate the long-term effectiveness of the live attenuated herpes zoster vaccine within 6 years after vaccination. We plan to select 24,740 participants who were non-herpes zoster cases in the modified Full Analysis Set for Efficacy (E-mFAS) from the Phase III Clinical Trial (NCT04334577) of the live attenuated herpes zoster vaccine manufactured by Changchun BCHT Biotechnology Co. conducted during 2020-2021. In the original Phase III Clinical Trial, the participants were randomly assigned to the vaccine group and the placebo group at a 1:1 ratio to receive one dose of the live attenuated herpes zoster vaccine (with varicella-zoster virus \>=4.3 lg PFU per 0.5 mL dose) or one dose of placebo (with no varicella-zoster virus component), respectively. This study uses a stage-based design. In Stage 1, participants originally assigned to the vaccine group and those originally assigned to the placebo group will be compared to assess the cumulative incidence of herpes zoster from the end of the original Phase III Clinical Trial in July 2021 to the marketing authorization of the vaccine in China in June 2023. In Stage 2, after marketing authorization of the vaccine in China in June 2023, a large proportion of the participants originally assigned to the placebo group received catch-up vaccination and thereby formed a catch-up vaccination group. These stage-specific groups will be compared to evaluate the relative waning of protection in participants who received catch-up vaccination compared with participants vaccinated in the original Phase III Clinical Trial. In addition, among participants originally assigned to the placebo group who received catch-up vaccination, the incidence of herpes zoster during the post-catch-up vaccination period will be compared with the incidence during their earlier placebo period before catch-up vaccination, in order to evaluate the relative risk of herpes zoster under vaccinated versus placebo exposure. For this study, telephone surveys will be conducted using a standardized questionnaire to collect data on herpes zoster occurrence from participants, with verbal informed consent obtained prior to the survey. Face-to-face interviews will also be conducted to verify reported herpes zoster cases. Moreover, their past medical history and lifestyle information will be collected.