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.