Estimation of the Time-Varying Reproduction Number of 2019-nCoV Outbreak in China

Background: The 2019-nCoV outbreak in Wuhan, China has attracted world-wide attention. As of February 5, 2020, a total of 24433 cases of novel coronavirus-infected pneumonia associated with 2019-nCov were confirmed by the National Health Commission of China. Methods: Three approaches, namely Poisson likelihood-based method (ML), exponential growth rate-based method (EGR) and stochastic Susceptible-Infected-Removed dynamic model-based method (SIR), were implemented to estimate the basic and controlled reproduction numbers. Results: A total of 71 chains of transmission together with dates of symptoms onset and 67 dates of infections were identified among 5405 confirmed cases outside Hubei as reported by February 2, 2020. Based on this information, we find the serial interval having an average of 4.41 days with a standard deviation of 3.17 days and the infectious period having an average of 10.91 days with a standard deviation of 3.95 days. Although the estimated controlled reproduction numbers R_c produced by all three methods in all different regions are significantly smaller compared with the basic reproduction numbers R_0, they are still greater than one. Conclusions: Although the controlled reproduction number is declining, it is still larger than one. Additional efforts are needed to further reduce the R_c to below one in order to end the current epidemic.