Fig. 3.

Simulations of the model (3.9) showing the number of all individuals in two cities as a function of time using the parameter values in Table 1 with $\beta =0.6$ and ${\mathcal{R}}_0^{\prime }=0.72<1$: (a)–(d) the profiles of all populations in city 1; (e)–(h) the profiles of all populations in city 2.