Super-spreading events initiated the exponential growth phase of COVID-19 with ℛ ₀ higher than initially estimated

The basic reproduction number ℛ ₀ of the coronavirus disease 2019 has been estimated to range between 2 and 4. Here we used a SEIR model that properly accounts for the distribution of the latent period and, based on empirical estimates of the doubling time in the near-exponential phases of epidemic progression in several locations, we estimated that ℛ ₀ lies in the range 4.7–11.4. We explained this discrepancy by performing stochastic simulations of model dynamics in a population with a small proportion of super-spreaders. The simulations revealed two-phase dynamics, in which an initial phase of relatively slow epidemic progression diverts to a faster phase upon appearance of infectious super-spreaders. Early estimates obtained for this initial phase may suggest lower ℛ ₀ .