The SIS Model
Some infections, for example the group of those responsible for the common cold, do not confer any long lasting immunity. Such infections do not have a recovered state and individuals become susceptible again after infection.
We have the model:
Note that denoting with N the total population it holds that: it follows that:
i.e. the dynamics of infectious is ruled by a logistic equation, so that :
Read more about this topic: Compartmental Models In Epidemiology
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