Simulating Retarded SEIRS model for COVID-19: will the second epidemic happen?

In this paper, we want to simulate the COVID-19 epidemic according to the Retarded SEIRS model. One of the main questions in the human mind is whether the COVID-19 epidemic will happen again. Therefore, a criterion must be set for the occurrence or non-occurrence of the disease. With the Retarded SEIRS model and this criterion, we can predict whether the Covid-19 will re-emerge. So far, a large number of researches that have been presented in scientific groups or communities have been based on the SIR or SEIR model. But we assume that each recovered individual is immune to the disease for a limited time, and then will be susceptible again. As we know, this assumption was also true for SARS.