We provide an easy and accurate method for approximating the reproduction number R 0 defined in an SIR epidemic model. At first, we present a formula extracting the exact R 0 in case of constant rates of infection and recovery assumed in an SIR model. Then, we proceed proposing an exponential fitting to various data taken from the real-world epidemics. Certain applications for current COVID outbreak are considered, and figures describing the fluctuation of R 0 in various countries are given.
Keywords: COVID‐19 outbreak; SIR epidemic model; exponential fitting; initial value problem.
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