[Study of transmissibility of 2019-nCoV Omicron variant in Beijing]

Objective: To evaluate the transmissibility of 2019-nCoV Omicron variant under the current prevention and control strategy in Beijing, and provide evidence for the prevention and control of COVID-19. Methods: The information of 78 Omicron variant infection cases involved in clear transmission chains in Beijing during 7-25 March, 2022 were collected, the incubation period and serial interval of the disease were fitted by using Gamma and Weibull distribution. Markov Chain Monte Carlo approach was used to estimate the time-varying reproduction number (R). Results: The median of the incubation period (Q₁, Q₃) of Omicron variant infection was 4.0 (3.0, 6.0) days, and the serial interval was 3.0 (2.0, 5.0) days. The median of the serial interval (Q₁, Q₃) was 2.0 (1.0, 4.0) days in unvaccinated cases and 4.0 (2.0, 6.0) days in vaccinated cases (Z=-2.12, P=0.034), and 2.0 (1.5, 3.0) days in children and 4.0 (2.0, 6.0) days in adults, respectively (Z=-2.02,P=0.044), the differences were significant. The mean of R was estimated to be 4.98 (95%CI: 2.22-9.04) for Omicron variant in this epidemic. Conclusion: Omicron variant has stronger transmissibility compared with Delta variant. It is necessary to strengthen the routine prevention and control COVID-19, promote the vaccination and pay close attention to susceptible population, such as children.