“…Since spatial diffusion does not change the number and location of constant equilibria, we can establish the existence of nonnegative equilibria of (1.4), which is consistent with the results in [18]. (i) the model always has the disease-free equilibrium E 0 = (λ/d, 0, 0, 0); (ii) if the basic reproductive number R 0 > 1, then there exists an immune-free equilibrium E 1 = (u 1 , w 1 , v 1 , 0), where…”