Background and aims: Iran had passed the third peak of COVID-19 pandemic, and was probably
witnessing the fourth peak at the time of this study. This study aimed to model the spread of COVID-19
in Iran in order to predict the short-term future trend of COVID-19 from April 23, 2021 to May 7, 2021.
Methods: In this study, a modified SEIR epidemic spread model was proposed and the data on the
number of cases reported by Iranian government from February 20, 2020 to April 23, 2021 were used
to fit the proposed model to the reported data using particle swarm optimization (PSO) algorithm. Then
the short-term future trend of COVID-19 cases were predicted by using the estimated parameters.
Results: The results indicated that the effective reproduction number increased in Nowruz (i.e., Persian
New Year, 1400) and it was estimated to be 1.28 in the given period. According to the results from the
short-term prediction of COVID-19 cases, the number of active confirmed cases in the fourth peak was
estimated to be 516 411 cases on May 2, 2021.
Conclusion: Following the results from our short-term prediction, implementing strict social distancing
policies was found absolutely necessary for relieving the Iran’s health care system of the tremendous
burden of COVID-19.