An updated estimation of the risk of transmission of the novel coronavirus (2019-nCov)

Tang, Biao; Bragazzi, Nicola Luigi; Li, Qian; Tang, Sanyi; Xiao, Yanni; Wu, Jianhong

To estimate the effective daily reproduction ratio, we initially get the time-dependent contact rate cðtÞ and d I ðtÞ as Fig. 1(a) . Using the discrete values of contact rate cðtÞ and diagnose rate d I ðtÞ, we can calculate the effective daily reproduction ratio, shown in Fig. 1(b) . It follows that under the strict prevention and control measures, the effective daily reproduction ratio R d ðtÞ has been less than 1 since January 26th , 2020, that is, the number of new infections has begun to decline. Note that the effective daily reproduction ratio declined from January 23rd , 2020 to January 25th , 2020, as a combination of the restrictive measures, including the lock-down of Wuhan, contact tracing followed by quarantine and isolation, that have been implemented. In practice, this time variation of the contact and diagnose rates leads to sub-exponential rather than exponential growth dynamics, and hence provides better estimates of epidemic size compared to fully exponential growth models. We refer to (Pell, Kuang, Viboud, & Chowell, 2018; Smirnova & Chowell, 2017) for earlier studies on sub-exponential growth of modern epidemics.