# SIS model

Author: Simon Frost

Date: 2018-07-12

### Description

The susceptible-infected-susceptible (SIS) model is one of the simplest models that has an endemic equilibrium. Susceptible individuals, $S$, are infected by infected individuals, $I$, at a per-capita rate $\beta I$, and infected individuals recover at a per-capita rate $\gamma$ to become susceptible again.