Abstract
BACKGROUND: WSK-V102C is a trimeric recombinant protein COVID-19 vaccine against XBB1.5/BA.5/Delta variants that was approved for emergency use in China in June 2023. We evaluated WSK-V102C vaccine effectiveness (VE) against SARS CoV-2 JN.1 symptomatic infection among adults aged ≥ 60 years using an observational prospective cohort study. METHODS: Participants were recruited in Xixian New Area, Shaanxi Province in December 2023 and January 2024 and were offered the choice of vaccination or no vaccination. Vaccination was defined by receipt of one dose of WSK-V102C vaccine; follow-up was active, involving periodic PCR testing for infection - weekly for three months and every two weeks until the six-to-seven month follow-up was completed. The primary outcome of interest was laboratory-proven symptomatic SARS-CoV-2 infection. Cox proportional hazards regression modelling was used to estimate adjusted hazard ratios (aHR) for estimation of adjusted vaccine effectiveness (aVE), calculated as (1 - adjusted hazard ratio) multiplied by 100%, with 95% confidence intervals (CIs). RESULTS: Among 6 313 participants meeting inclusion criteria, 3 216 received WSK-V102C and 3 097 did not receive WSK-V102C (or other COVID-19 vaccine) during the study period. The mean (SD) age of participants was 69.6 (6.4) years; the median follow-up time was 160 (IQR 153-166) days; 140 (2.2%) participants tested positive for SARS-CoV-2 nucleic acid, with 63 having symptomatic infection. No infected subjects were hospitalized or died. For prevention of symptomatic SARS-CoV-2 infection, all-ages aVE was 42.0% (95%CI: 3.5%, 65.1%); in 60-74-year-olds aVE was 50.1% (95%CI: 8.8%, 72.7%); and in individuals 75 years old and above, aVE was 10.6% (95%CI: -139.0%, 66.6%). Duration of symptoms was longer in unvaccinated subjects. Rates of laboratory-proven infection, including asymptomatic infection, were not different by vaccination status. CONCLUSIONS: Among individuals aged ≥ 60 years, WSK-V102C vaccination provided moderate protection against JN.1 symptomatic infection within 6 months, suggesting that older people can benefit from use of this vaccine.