Effectiveness of mRNA and inactivated COVID-19 vaccines: A test-negative study in an infection-naïve Hong Kong population

OBJECTIVE: Assess real-world effectiveness of vaccines against COVID-19. METHODS: A test-negative study was conducted in January-May 2022 during an Omicron BA.2 wave in Hong Kong. COVID-19 was identified by RT-PCR. 1–1 case-control matching was based on propensity score with vaccine effectiveness adjusted for confounders. RESULTS: Altogether, 1781 cases and 1737 controls aged 3–105 years were analysed. The mean lag time from the last dose of vaccination to testing for SARS-CoV-2 was 133.9 (SD: 84.4) days. Two doses of either vaccine within 180 days offered a low effectiveness against COVID-19 of all severity combined (VE(adj) [95% CI] for BNT162b2: 27.0% [4.2–44.5], CoronaVac: 22.9% [1.3–39.7]), and further decreased after 180 days. Two doses of CoronaVac were poorly protective 39.5% [4.9–62.5] against severe diseases for age ≥ 60 years, but the effectiveness increased substantially after the third dose (79.1% [25.7–96.7]). Two doses of BNT162b2 protected age ≥ 60 years against severe diseases (79.3% [47.2, 93.9]); however, the uptake was not high enough to assess three doses. CONCLUSIONS: The current real-world analysis indicates a high vaccine effectiveness of three doses of inactivated virus (CoronaVac) vaccines against Omicron variant, whereas the effectiveness of two doses is suboptimal.