Early dynamics of transmission and control of COVID-19: a mathematical modelling study

TLDR

An outbreak of SARS‑CoV‑2 had resulted in 46,997 confirmed cases worldwide by 13 February 2020. The study aimed to characterize early transmission dynamics of COVID‑19 and assess the effectiveness of control measures in preventing sustained spread to new regions. Using a stochastic transmission model fitted to Wuhan and international case data, the authors estimated time‑varying reproduction numbers and calculated the probability that imported cases would spark outbreaks elsewhere. They found the median reproduction number fell from 2.35 to 1.05 after travel restrictions, and that in areas with Wuhan‑like transmission potential, more than half of the time a cluster of at least four imported cases would establish, though many chains initially fail yet could later ignite new outbreaks. Funding was provided by the Wellcome Trust, HDR UK, Gates Foundation, and NIHR.

Abstract

Abstract Background An outbreak of the novel coronavirus SARS-CoV-2 has led to 46,997 confirmed cases as of 13 th February 2020. Understanding the early transmission dynamics of the infection and evaluating the effectiveness of control measures is crucial for assessing the potential for sustained transmission to occur in new areas. Methods We combined a stochastic transmission model with data on cases of novel coronavirus disease (COVID-19) in Wuhan and international cases that originated in Wuhan to estimate how transmission had varied over time during January and February 2020. Based on these estimates, we then calculated the probability that newly introduced cases might generate outbreaks in other areas. Findings We estimated that the median daily reproduction number, R t , declined from 2.35 (95% CI: 1.15-4.77) one week before travel restrictions were introduced on 23 rd January to 1.05 (95% CI: 0.413-2.39) one week after. Based on our estimates of R t ,we calculated that in locations with similar transmission potential as Wuhan in early January, once there are at least four independently introduced cases, there is a more than 50% chance the infection will establish within that population. Interpretation Our results show that COVID-19 transmission likely declined in Wuhan during late January 2020, coinciding with the introduction of control measures. As more cases arrive in international locations with similar transmission potential to Wuhan pre-control, it is likely many chains of transmission will fail to establish initially, but may still cause new outbreaks eventually. Funding Wellcome Trust (206250/Z/17/Z, 210758/Z/18/Z), HDR UK (MR/S003975/1), Gates Foundation (INV-003174), NIHR (16/137/109)