Before revision:  In the first part, we have pointed out a major over-simplification, i.e., assumption of variation of the time derivatives of the variables with the linear  powers of the individual variables and introduced two new parameters to incorporate further non-linearity to the number of infected people in the model.
After revision:  In the first part, we have pointed out a major over-simplification, i.e., assumption of variation of the time derivatives of the variables with the linear or quadratic powers of the individual variables and introduced two new parameters to incorporate further non-linearity to the number of infected people in the model.