Daily multiplication coefficient predicted by the model and estimated from data. (A) Dependence of the daily multiplication coefficient, θ, on the basic reproduction number . Dotted lines guide the eye to relate and β coming from data for China before and after quarantine (‘Q’) and for several European countries and the US based on last-week data. (B) Epidemic dynamics in selected countries with high number of cumulative confirmed cases of COVID-19 based on data from Johns Hopkins University (JHU) Center for Systems Science and Engineering (CSSE) [16]. Value of initial θ for China is estimated based on 7 or 14 days of the early exponential phase; current θ is estimated for countries being in the exponential phase based on last-week data (7 days since March 14 to March 20, 2020). Introduction of quarantine in China (January 23) is marked with ‘Q’. The range of values of is computed assuming that 1∕γ is in between 3 and 5 days.