Transmission potential of mpox in mainland China, June-July 2023: estimating reproduction number during the initial phase of the epidemic.

Despite reporting very few mpox cases in early 2023, mainland China observed a surge of over 500 cases during the summer. Amid ambiguous prevention strategies and stigma surrounding mpox transmission, the epidemic silently escalated. This study aims to quantify the scale of the mpox epidemic and assess the transmission dynamics of the virus by estimating the effective reproduction number ( R e ) during its early phase. Publicly available data were aggregated to obtain daily mpox case counts in mainland China, and the R e value was estimated using an exponential growth model. The mean R e value was found to be 1.57 (95% credible interval [1.38-1.78]), suggesting a case doubling time of approximately 2 weeks. This estimate was compared with R e values from 16 other countries' national outbreaks in 2022 that had cumulative case count exceeding 700 symptomatic cases by the end of that year. The R e estimates for these outbreaks ranged from 1.13 for Portugal to 2.31 for Colombia. The pooled mean R e was 1.49 (95% credible interval [1.32-1.67]), which aligns closely with the R e for mainland China. These findings underscore the need for immediate and effective control measures including targeted vaccination campaigns to mitigate the further spread and impact of the epidemic.