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Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study

Our take —

Early major study of COVID-19 estimating the final size of COVID-19 in Wuhan and further projecting the spread within and outside mainland China. Findings from this study support ongoing, self-sustained outbreaks in other metropolitan areas due to the high basic reproductive number (estimated at 2.68), and the exportation of pre-symptomatic cases, to other large cities, from Wuhan early in the epidemic. Large scale public health interventions will be needed, globally, to curb the epidemic. Due to the paucity of data at the time of publication, estimates of key epidemic parameters are likely to change as data within and outside mainland China are updated.

Study design


Study population and setting

Using data from December 31, 2019 to January 28, 2020 on the number of cases exported internationally from Wuhan, authors estimated the size of the epidemic in Wuhan and forecasted the national and global spread of COVID-19 accounting for the Greater Wuhan region quarantine and other non-pharmaceutical interventions.

Summary of Main Findings

Using data on monthly flight bookings from the Official Aviation Guide (OAG) and confirmed case counts from reports published by the Chinese Center for Disease Control and Prevention (CDC), authors estimated the number of secondary cases one case would infect in a completely susceptible population, (R0), for COVID-19 was 2.68 (95%CI: 2.47-2.86) as of January 25, 2020, and the time it took for the epidemic to double in size was 6.4 days (95% CI: 5.8-7.1). Authors further estimated 0.40% (95% CI: 0.20-0.69%) of the 19 million people in Greater Wuhan had been infected as of January 25, 2020.

Study Strengths

This study provides early estimates of the R0 of COVID-19 and other important COVID-19 epidemic parameters. The study pools information from multiple sources, including line list data from the Chinese CDC and up to date mobility data from OAG and Tencent.


This was one of the early papers published about COVID-19; due to the uncertainty surrounding the pathogen, used serial interval estimates based on SARS which are longer than current estimates for COVID-19 (roughly 8 versus 4 days) . In addition, in the analysis, authors assumed travel behavior was not affected by disease status, and that all infections would eventually be symptomatic.

Value added

One of the first major studies published about the COVID-19 outbreak in Wuhan. The study inferred the outbreak size within Wuhan and forecasted the spread of COVID-19 within and outside mainland China in the absence of a robust and reliable line list data characterizing the epidemiology of the pathogen.