Mathematical and numerical analysis of a SEVIR-S model for adenovirus with immunity waning and reinfection effects

In this study, we proposed a modified SEVIR-S (susceptible, exposed, vaccinated, infected, recovered) model for the transmission dynamics of adenovirus by incorporating the effects of immunity waning and reinfection. Unlike the classical SEVIR framework, the extended model accounted for the possibility that recovered individuals may lose immunity over time and become susceptible again — a critical feature for accurately modeling diseases like adenovirus. To better capture the disease's memory effects and temporal dynamics, the model used the fractal-fractional Caputo-Fabrizio derivative with a power-law kernel. The paper analyzed the model's existence and stability using fixed point theory and Hyers-Ulam (H-U) stability. Furthermore, both the disease-free and endemic equilibrium points and their stability were analyzed. Also, the basic reproduction number was provided. The findings were validated through numerical simulations using an extended Adams-Bashforth method.