Objective  To estimate the transmission dynamics parameters of Omicron BA.5.2 variant and provide a scientific evidence for understanding the infectivity of Omicron BA.5.2.

  Methods  The data of infection time, onset time and first positive sampling time of the infection cases with clear infection relationship in two outbreaks in Jingzhou were collected by using self-designed forms. The obtained data were fitted with log-normal distribution, gamma distribution and gamma distribution to calculate incubation period, generation time (GT), and serial interval (SI). The exponential growth model (EG) and the maximum likelihood estimation method (ML) were used to calculate R0, respectively. The fitted value with the larger R² was used as the R0 estimate.

  Results  In the 2 outbreaks in Jingzhou, outbreak A was caused by the imported virus spread in local population mainly through people's living, dining, amusing and working together, showing a common social transmission pattern. Outbreak B occurred in a wholesale market, which was caused by an infection case who had stay in the market for 3 hours and subsequent rapid transmission in market workers and their close contacts, showing a clustered transmission pattern. A total of 52 cases in 39 pairs of primary and secondary cases in the 2 outbreaks were included for the estimations of incubation period, GT and SI. The median of incubation period was 2.52 days (44 cases, 1.32−4.84 days), the median of SI was 2.13 days (37 cases, 1.63−2.64 days), and the median of GT was 1.91 days (21 cases, 1.05–3.15 days). The optimal fitting models of outbreak A and outbreak B were all EG models, and the corresponding R² were 0.62 and 0.88, respectively. The fitted R0s of outbreak A and outbreak B were 5.33 (95%CI: 2.08–13.44) and 22.58 (95%CI: 7.23–91.36), respectively. In some cases, the shortest interval (20−21 hours) between exposure and detection was observed.

  Conclusion  Omicron BA.5.2 variant has the characteristics of short incubation period, rapid transmission speed and strong infectivity. In crowded places, Omicron BA.5.2 variant has very strong transmission ability.