Abstract
The complete lifting of travel restrictions to KSA takes place after 3rd of January 2021. There are fears that KSA will confront a new COVID-19 wave, especially when the most of countries that resumed the international flights are suffering now from the second surge. Fortunately, more than one Covid-19 Vaccine have been rolled out. However, herd immunity could be reached only through widespread vaccination. COVID-19 vaccines need more time to be properly protective, especially in front of people refusing to get vaccinated. A modified multi-stage SEIR model, with distinct reproductive numbers corresponding to before and after lockdown is employed to predict the potential of a new pandemic wave. First, the two-stage model employed to find the best fitting for the reproductive numbers. Then, the model is extended to three-stage one to investigate the relaxation. However, the modified model detects a second wave in early stage from 28th May to 17th June 2020 before even succeeding controlling the first outbreak. Subsequently, the four-stage SEIR model is used to predict the end of the second wave. Moreover, the model is employed to test the potential of a new pandemic surge after the international flights are resumed. (C)2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.