## 2 Model  
According to the classical compartment model of infectious diseases, the total population of an area is assumed to be \(N\), the individuals within a population who can be classified susceptible is \(S\), the number of exposed individuals is \(E\), the number of mildly infected individuals is \(I_{1}\), the number of severely infected individuals is \(I_{2}\), the number of hospitalized and isolated patients with mild infections is \(H_{1}\), the number of hospitalizedand isolated patients with severe infections is \(H_{2}\), the number of recovered cases is \(R\) and the death rate is \(D\). In this study, it was assumed that the population was well mixed and had a fixed number of individuals and the vaccination of susceptible individuals was not considered. The probability of susceptible individuals becoming infected is independent of their age, gender, etc. This paper only considered contact infection, not immune loss. It was also supposed that the susceptible individuals would be infected with a probability of \(\beta\) after contact with mildly or severely infected individuals. The decreasing proportion of infectivity during the incubation period was assumed to be \(\eta(0<\eta<1)\) and the incidence rate of exposed individuals was \(\alpha\). When exposed individuals showed symptoms, they had a probability of \(q\) of becoming mildly infected or a probability of \(1-q\) of becoming severely infected. \(v_{1}\) and \(v_{2}\) represent the isolation rates of hospitalized mildly and severely infected individuals, respectively. The model parameters are shown in Table 1 and the transformation relationship of populations is shown in Figure 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Name** & **Interpretation** & **Value** & **Reference** \\ \hline \(\beta\) & Contact rate & Probability of a susceptible individual coming into contact with & & \\  & & an exposed or infected individual & & \\ \hline \(\alpha\) & Incidence rate & Incidence rate of exposed individuals & 0.25 & [35] \\ \hline \(\eta\) & Infection rate & Infection rate of exposed individuals & 0.5 & [35] \\ \hline \(q\) & Proportion & Proportion of exposed individuals who became mildly infected & & \\  & & individuals & 0.8 & Assumed \\ \hline \(v_{1}\) & Isolation rate & Isolation rate of mildly infected individuals & [0.1, 0.8] & Assumed \\ \hline \(v_{2}\) & Isolation rate & Isolation rate of severely infected individuals & [0.1, 0.8] & Assumed \\ \hline \(r_{I_{1}}\) & Self-healing rate & Self-healing rate of mildly infected individuals & 0.067 & Assumed \\ \hline \(r_{I_{2}}\) & Self-healing rate & Self-healing rate of severely infected individuals & 0 & Assumed \\ \hline \(r_{H_{1}}\) & Cure rate & Cure rate of mildly isolated individuals & 0.067 & Assumed \\ \hline \(r_{H_{2}}\) & Cure rate & Cure rate of severely isolated individuals & [0, 1] & Assumed \\ \hline \(d_{I_{1}}\) & Mortality & Mortality rate of mildly infected individuals & 0 & Assumed \\ \hline \(d_{I_{2}}\) & Mortality & Mortality rate of severely infected individuals & 0.033 & Assumed \\ \hline \(d_{H_{1}}\) & Mortality & Mortality rate of mildly infected individual who were isolated & 0 & Assumed \\ \hline \(d_{H_{2}}\) & Mortality & Mortality rate of severely infected individual who were isolated & [0, 1] & Assumed \\ \hline \(T_{I_{1}}\) & Duration & Duration of self-healing and death in mildly infected individuals & 15 & Assumed \\ \hline \(T_{I_{2}}\) & Duration & Duration of self-healing and death in severely infected individuals & 30 & Assumed \\ \hline \(T_{H_{1}}\) & Duration & Duration of cure and death in mildly infected individuals who & 15 & Assumed \\ \hline \(T_{H_{2}}\) & Duration & Duration of cure and death in severely infected individuals who & 30 & Assumed \\ \hline \(M\) & Medical resource & Number of beds needed for severely infected individuals & [0, 10\({}^{7}\)] & Assumed \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Descriptions of the variables and parameters.