Stability and Hopf Bifurcation Analysis of an Age-Structured SVIRS Epidemic Model with Temporary Immunity

In this paper, we investigate an SVIRS epidemic model that incorporates both temporary immunity and an age-structured recovery process. By reformulating the system as a nondensely defined abstract Cauchy problem, we establish the existence and uniqueness of solutions and derive the basic reproduction number. The stability of the equilibria is analyzed through the associated characteristic equations, and the occurrence of Hopf bifurcation near the endemic equilibrium is rigorously demonstrated. Our theoretical results reveal that temporary immunity plays a crucial role in shaping the stability of the endemic state. Finally, numerical simulations are carried out to verify and illustrate the analytical findings.