  In this work we study a modified Susceptible-Infected-Susceptible (SIS) model
in which the infection rate $\lambda$ decays exponentially with the number of
reinfections $n$, saturating after $n=l$. We find a critical decaying rate
$\epsilon_{c}(l)$ above which a finite fraction of the population becomes
permanently infected. From the mean-field solution and computer simulations on
hypercubic lattices we find evidences that the upper critical dimension is 6
like in the SIR model, which can be mapped in ordinary percolation.
