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An SIS Model with Importation and Removal
Sep 2026 · International Journal of Bifurcation and Chaos in Applied Sciences and Engineering · 0 citations
Abstract
The Susceptible–Infectious–Susceptible (SIS) model is a classical model for describing the spread of diseases without permanent immunity and has been studied by many authors. In this paper, we characterize all topologically distinct phase portraits in the Poincaré disc for a particular SIS epidemic model with a constant importation or removal rate of infected individuals. Thus, for the first time, we provide a complete description of the qualitative dynamics of all orbits of this system, including those tending to or coming from infinity.