Abstract

In December 2019, a novel coronavirus (2019-nCoV) is thought to have emerged into the human population in Wuhan, China. The number of identified cases in Wuhan has increased rapidly since, and cases have been identified in other Chinese cities and other countries (as of 23 January 2020). We fitted a transmission model to reported case information up to 21 January to estimate key epidemiological measures, and to predict the possible course of the epidemic, as the potential impact of travel restrictions into and from Wuhan. We estimate the basic reproduction number of the infection (R_0) to be 3.8 (95% confidence interval, 3.6-4.0), indicating that 72-75% of transmissions must be prevented by control measures for infections to stop increasing. We estimate that only 5.1% (95%CI, 4.8-5.5) of infections in Wuhan are identified, and by 21 January a total of 11,341 people (prediction interval, 9,217-14,245) had been infected in Wuhan since the start of the year. Should the epidemic continue unabated in Wuhan, we predict the epidemic in Wuhan will be substantially larger by 4 February (191,529 infections; prediction interval, 132,751-273,649), infection will be established in other Chinese cities, and importations to other countries will be more frequent. Our model suggests that travel restrictions from and to Wuhan city are unlikely to be effective in halting transmission across China; with a 99% effective reduction in travel, the size of the epidemic outside of Wuhan may only be reduced by 24.9% on 4 February. Our findings are critically dependent on the assumptions underpinning our model, and the timing and reporting of confirmed cases, and there is considerable uncertainty associated with the outbreak at this early stage. With these caveats in mind, our work suggests that a basic reproductive number for this 2019-nCoV outbreak is higher compared to other emergent coronaviruses, suggesting that containment or control of this pathogen may be substantially more difficult.