Estimation of the serial interval and basic reproduction number of COVID-19 in Qom, Iran, and three other countries: A data-driven analysis in the early phase of the outbreak.

The outbreak of COVID-19 was first reported from China, and on 19 February 2020, the first case was confirmed in Qom, Iran. The basic reproduction number (R ) of infection is variable in different populations and periods. This study aimed to estimate the R of COVID-19 in Qom, Iran, and compare it with that in other countries. For estimation of the serial interval, we used data of the 51 confirmed cases of COVID-19 and their 318 close contacts in Qom, Iran. The number of confirmed cases daily in the early phase of the outbreak and estimated serial interval were used for R estimation. We used the time-varying method as a method with the least bias to estimate R in Qom, Iran, and in China, Italy and South Korea. The serial interval was estimated with a gamma distribution, a mean of 4.55 days and a standard deviation of 3.30 days for the COVID-19 epidemic based on Qom data. The R in this study was estimated to be between 2 and 3 in Qom. Of the four countries studied, the lowest R was estimated in South Korea (1.5-2) and the highest in Iran (4-5). Sensitivity analyses demonstrated that R is sensitive to the applied mean generation time. To the best of the authors' knowledge, this study is the first to estimate R in Qom. To control the epidemic, the reproduction number should be reduced by decreasing the contact rate, decreasing the transmission probability and decreasing the duration of the infectious period.