Modelling of outbreaks of SARS-CoV-2 Omicron variants after easing Dynamic Zero-COVID strategy in mainland China

Background: China lifted strict non-pharmacological interventions (NPIs) to prevent outbreaks of SARS-CoV-2 Omicron variants in December 2022. Relatively low levels of immunity and of vaccine booster coverage in the Chinese population raise concerns that future outbreaks will rapidly result in high rates of death and severe illness and will overwhelm health services. Methods: This was a compartmental, discrete-time population dynamic model. It compared projected deaths and hospitalisation under various scenarios, including booster vaccine coverage and strictness of NPIs. Results: We projected between 268,300 to 398,700 COVID-19 deaths, and peak numbers of hospitalised severe/critical cases between 3.2 to 6.4 per 10,000 population, before the outbreak wave recedes by February 2023. The COVID-19 deaths are reduced by 8% and 30%, respectively, under the weak and strict NPI scenarios, compared with the scenario without NPI measures. Early achievement of high coverage of three vaccine doses will further reduce COVID-19 deaths. Conclusion: We projected fewer COVID-19 deaths and hospitalisations than some other models have. Rapid expansion of booster vaccine coverage will only be effective if combined with strict NPIs and/or the high coverage of booster vaccination could be achieved early.