Fig. 1.

The flowchart of the transmission dynamics model, where the population is stratified by susceptible ($S$), exposed ($E$), infectious but asymptomatic ($A$), infectious with symptoms ($I$), and removed ($R$). The solid lines indicate the transmissions inside a city and dash lines show the transmissions between two cities. The dash line connecting $S$ in city $x$ and $E$ in city $y$ means some of the susceptible population in city $x$, who are in contact with the mobile infectious population during the travel from city $x$ to city $y$, become exposed in city $y$. Similarly, the dash line connecting $S$ in city $y$ and $E$ in city $x$ means some of the susceptible population in city $y$ become exposed in city $x$ because of the infection during the travel from city $y$ to city $x$.