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 February 19, 2020, the first case was confirmed in Qom, Iran. The basic reproduction number (R0 ) of infection is variable in different populations and periods. The present study aimed to estimate the R0 of COVID-19 in Qom, Iran and compare it with 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 the Qom, Iran. The daily number of confirmed cases in the early phase of the outbreak and estimated serial interval were used for R0 estimation. We used the time-varying method as a method with the least bias to estimate R0 in Qom, Iran, China, Italy, and South Korea. The serial interval was estimated with gamma distribution, mean of 4.55 days and a standard deviation of 3.30 days for the COVID-19 epidemic based on Qom data. The number of R0 in the present study was estimated to be between 2 and 3 in Qom. Of the four countries studied, the lowest R0 was estimated for South Korea (1.5-2) and the highest for Iran (4-5). Sensitivity analyses demonstrated that R0 is sensitive to the applied mean generation time. To the best of the authors' knowledge, the current study is the first to estimate R0 number in Qom. To control the epidemic, the number of reproduction number should be reduced by decreasing the contact rate, decreasing transmission probability and decreasing the duration of the infectious period.