Interpretation of the Basic and Effective Reproduction Number

In epidemiology, the basic reproduction number (R(0)) is a term that describes the expected number of infections generated by 1 case in a susceptible population. At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, R(0) was frequently referenced by the public health community and the wider public. However, this metric is often misused or misinterpreted. Moreover, the complexity of the process of estimating R(0) has caused difficulties for a substantial number of researchers. In this article, in order to increase the accessibility of this concept, we address several misconceptions related to the threshold characteristics of R(0) and the effective reproduction number (R(t)). Moreover, the appropriate interpretation of the metrics is discussed. R(0) should be considered as a population-averaged value that pools the contact structure according to a stochastic transmission process. Furthermore, it is necessary to understand the unavoidable time lag for R(t) due to the incubation period of the disease.