“…Theoretical results of discrete epidemic models mainly focus on these aspects, including the computation of the basic reproduction number [8,18,19], the comparison between continuous-time epidemic models and discrete-time epidemic models [10,20], the local stability and global stability of the disease-free equilibrium and endemic equilibrium [6,7,9,11,15,16,21], the extinction, persistence, and permanence of a disease [12,[22][23][24][25], periodic systems [8,19,26], bifurcations and chaos phenomena [1,7,9,13,14,17,25,27,28], and so on. In particular, these papers about the bifurcation analysis of discrete epidemic model mainly involve the conditions on the existence of codimension-one bifurcations, such as fold bifurcation, flip bifurcation, Neimark-Sacker bifurcation [1,7,9,25,27,28], and so on, which were derived by using the center manifold theorem and bifurcation theory.…”