The Novel Coronavirus, 2019-nCoV, is Highly Contagious and More Infectious Than Initially Estimated

Steven Sanche; Yen Ting Lin; Chonggang Xu; Ethan Romero-Severson; Nick Hengartner; Ruian Ke

We note that in both approaches, we assumed perfect detection of infected cases outside of Hubei province, i.e. the dates of first arrival and the number of case counts are accurate. This could be a reasonable assumption to make for symptomatic individuals because of the intensive surveillance implemented in China, for example, tracking individuals' movement from digital transportation data (6). However, it is possible that a fraction of infected individuals, for example, individuals with mild or no symptoms (13), were not hospitalized, in which case we will underestimate the true size of the infected population in Wuhan. We undertook sensitivity analyses to investigate how our current estimates are affected by this issue using both approaches (see Supplementary Materials for detail). We found that if a proportion of cases remained undetected, the time of exponential initiation would be earlier than December 20, translating into a larger population of infected individuals in January, but the estimation of the growth rate remained the same. Overall, the convergence of the estimates of the exponential growth rate from the two approaches emphasizes the robustness of our estimates to modeldependent assumptions.