The Basic Reproduction Number and Prediction of the Epidemic Size of the Novel Coronavirus (COVID-19) in Shahroud, Iran

Background: In the first month of the epidemic in Iran, we had 19644 and 306 confirmed cases of COVID-19 in Iran and Shahroud, respectively. The aim of this study was to estimate the basic reproduction number (R0) of COVID-19 in the early stage of the epidemic and predict the expected number of new cases in Shahroud, Northeast of Iran. Methods: The R0 of COVID-19 was estimated using the serial interval distribution and the number of incidence cases in the early stage of the epidemic. The serial interval (mean ±standard deviation of 7·5±3·4) was fit with a gamma distribution. The probable incidence and cumulative incidence in the next 30 days were predicted using the assumption that daily incidence follows a Poisson distribution determined by daily infectiousness. Data analysis was done using “earlyR” and “projections” packages in R software. Findings: The maximum-likelihood value of R0 was 2.3 (95% confidence interval (CI): 1·9-2·9) for the COVID-19 epidemic in the early 14 days and decreased to 1.26 (95% CI: 1·1-1·4) by the end of the first month. The expected average number of new cases in Shahroud is 18·3±7·2 case/day, which means an estimated total of 550 (range: 388-710) new cases in the next 30 days. Interpretation: It is essential to reduce the R0 to values below 1. Therefore, we strongly recommend enforcing and continuing the current preventive measures, mass screening of suspected cases, restricting travel, and providing screening tests for a larger proportion of the population. Funding Statement: This Study is funded by Shahroud University of Medical Sciences (Grant No. 98126). Declaration of Interests: The authors declare that there is no conflict of interest. Ethics Approval Statement: The protocol of this study was reviewed and approved by the Institutional Review Board of Shahroud University of Medical Science (IR.SHMU.REC.1398.160).