“…If the basic reproduction number is larger than 1, then the disease-free equilibrium becomes unstable, and there is a unique endemic equilibrium. In most cases, the endemic equilibrium is locally or globally stable for all delays, whereas in some cases it is locally or globally stable only for small delay and Hopf bifurcation of periodic solutions may occur when the delay passes a certain critical value [17,19,20,23,25,29,35]. However, in our model any points (S 1 ,0,R 1 , .…”