Population-level effect of COVID-19 full vaccination coverage on transmission and mortality during Omicron variant dominance: a global longitudinal analysis

Abstract Aim Given the higher transmissibility of the SARS-CoV2 Omicron variant and associated concerns about reduced vaccine effectiveness, we assessed the population-level impact of COVID-19 vaccination on viral transmission and mortality during the period of global Omicron dominance. Subject and Methods : We used a longitudinal dataset of 110 countries over 16 months (January 2022 to April 2023), representing the period of global Omicron dominance. Applying country-level random effects regression models, we assessed the effect of lagged monthly full vaccination coverage on the monthly rates of new confirmed COVID-19 cases and deaths across these countries, adjusting for a wide range of country characteristics and policy interventions. We obtained the data from open-access databases, including the WHO COVID-19 Dashboard and the Oxford COVID-19 Government Response Tracker. Results On average, each 1 percentage point increase in full vaccination coverage was associated with a 1.4% reduction (95% confidence interval [CI]: 0.1–2.8%, p = 0.035) in the rate of new cases and a 5% reduction (95% CI: 3.6–6.4%, p < 0.001) in the rate of deaths. This protective effect was graded across levels of vaccination coverage: compared to countries with vaccination coverages < 50%, countries with coverages of 50–59%, 60–69%, 70–79% and ≥ 80% had 20.5% (95% CI: -16.4–45.7%, p = 0.20), 53.8% (22.6–72.5%, p = 0.003), 54.3% (15.5–75.3%, p = 0.01), and 69.6% (38.7–84.9%, p < 0.001) lower rates of new cases respectively, on average. Conclusion Our findings underscore the crucial role of vaccination in mitigating the impact of pandemics, particularly during the emergence of highly transmissible variants like Omicron.