Introduction
Since May 2022, the monkeypox (Mpox ) epidemic has caused 90618 cases and 157 deaths in 115 countries and regions [1]. At present, the epidemic in most areas is nearing its end. However, China was not affected by Mpox in 2022 because of its strict border quarantine and inbound traveler isolation policies, which had been applied since 2020 against coronavirus disease (COVID-19). Therefore, the spread of Mpox in mainland China is considerably lagging behind other countries. When the control policies were relieved in 2023, mainland China reported a significant increase in Mpox cases, with the first locally acquired case of Mpox confirmed in Beijing on May 31, 2023 [2]. Till 2023-09-30, there have been 1403 reported Mpox cases in mainland China, of which 222 cases were in Beijing [3]. Phylogenetic analysis also indicated the local strains transmitted in Beijing belonged to the West African lineage [4].
To estimate the development of Mpox epidemic and to design appropriate control measures, it is essential to understand the dynamics (i.e., effective reproduction number and dispersion number (k )) of Mpox transmission in mainland China. Effective reproduction number, denoted as R e, represents the average number of secondary cases caused by a primary case in a partly susceptible population [5]. R e >1 suggests the further infection is likely without stricter control measures.
In addition, the dispersion number k , representing the variation of the distribution of secondary cases, is an empirical measure of transmission heterogeneity [6,7]. A small k (i.e., k<1) indicates a high degree of transmission heterogeneity, indicating probability of a superspreading event (SSE) with one individual infecting a greater number of secondary cases than average. This was reported in the 1980-84 Mpox epidemic in West Africa [8]. Therefore, evaluation of transmission heterogeneity may also aid prevention efforts and reduce future infections.
In the past five months since the confirmation of the first Mpox in Beijing, there has not been a report of the transmission dynamics of this epidemic. The current study was to analyze the transmission characteristics based on an epidemiological report of confirmed daily Mpox cases from 05-31 to 06-21, 2023 in Beijing [4]. Specifically, we employed the instant-individual heterogeneity transmission model [6] to analyze the daily incidence to revealR e and k of Beijing Mpox epidemic in the first three weeks. As the daily incidence thereafter was not available, we simulated the subsequent infection size in Beijing from July to September to project subsequent transmission dynamics. Our results will shed light on the on-going Mpox epidemic in mainland China and provide reference for policy making and public response.