Estimation of the Time-Varying Reproduction Number of COVID-19 Outbreak in China

Abstract

Background: The 2019 novel coronavirus (2019-nCoV) outbreak in Wuhan, China has attracted world-wide attention. As of February 11, 2020, a total of 44,730 cases of pneumonia associated with the 2019-nCoV were confirmed by the National Health Commission (NHC) 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 5,405 confirmed cases outside Hubei as reported by February 2, 2020. Based on this information, we find the serial interval having an average of 4.27 days with a standard deviation of 3.44 days, the incubation period having an average of 5.33 days with a standard deviation of 3.36 days and the infectious period having an average of 10.91 days with a standard deviation of 3.95 days. The estimated controlled reproduction numbers, 𝑅_𝑐 , produced by all three methods in all analyzed regions of China are significantly smaller compared with the basic reproduction numbers 𝑅₀.

Conclusions: The controlled reproduction number is declining. It is lower than one in most regions of China, but still larger than one in Hubei Province. Sustained efforts are needed to further keep/reduce the 𝑅_𝑐 to below one in order to end the current epidemic.

Funding Statement: The authors stated that they have no financial relationships (regardless of amount of compensation) with any entities.

Declaration of Interests: The authors declare there is no conflict of interest.

Ethics Approval Statement: The authors stated this was not required.

Keywords: serial interval, incubation period, infectious period, reproduction rate