Discussion
This study estimated the transmission dynamics (i.e., effective reproduction number R e and dispersion numberk ) of Mpox in Beijing in the first three weeks of transmission for the first time. The effective reproduction numberR e was calculated to be 1.68 [95% HPD:1.12, 2.41] , which is higher than the threshold value of 1. And the dispersion number k was 2.57 [95% HPD: 0.54, 83.88], which is also greater than 1 and does not indicate a high risk of transmission heterogeneity.
Compared with the transmission of the West African lineage reported outside of China, our estimation of R e>1 for the Beijing epidemic is consistent with that of the England (R e = 1.60 (95% CI: 1.50, 1.70)), Portugal (R e =1.40 (95% CI: 1.20, 1.60)) and Spain (R e = 1.80 (95% CI: 1.70,2.0) ) in May to June of 2022 [5]. Our estimates of the first three weeks suggested that the Beijing Mpox epidemic would have additional infections after 2023-06-21, which was evidenced by the increase in reported new cases to 80 in July 2023 [3]. When certain measures were subsequently adopted, the reported new cases dropped to 54 in August and 42 in September, which corresponded to R e of 0.95-1.0, slightly under the threshold of 1, as revealed by our simulation. This also indicates that additional measures need to be taken to further reduce the transmissibility of Mpox in Beijing. .
Another interesting feature of Beijing Mpox epidemic is the homogenous transmission. We estimated k = 2.57, being above the critical value of 1, and estimated that 80% of secondary transmissions were likely to be caused by 25% of primary cases, which did not invoke the 20/80 rule [7]. Our finding was consistent with the epidemiological investigation which showed that the distribution of the close contact among the confirmed cases in Beijing was not skewed and no SSE was identified [4]. Similarly, another research about Mpox transmission in the United States in 2022 also reported absence of heterogeneity and no SSE identified [10].
In contrast, for the 1980-84 Mpox epidemic in West Africa, several SSEs were reported, which was closely related with the unrecognized or misdiagnosed cases that were later documented [8,11]. Besides, contemporary health-workers and the public have improved awareness against Mpox infection, which reduced the risk of infection or mis-diagnose and thereby reduced the chance of SSE [10]. In addition, the homogenous nature of the Mpox transmission in Beijing highlighted that more population-level intervention, for instance, vaccines, could be effective in reducing the transmissibility of the Mpox virus [7].
In conclusion, we assessed the transmission dynamics in the early stage of Mpox epidemic in Beijing, China. Our findings revealed super critical and homogeneous transmission of the Mpox epidemic in Beijing. Our results may provide reference for understanding and predicting of the on-going Mpox transmission in other regions of China and assess the effect of control measures.