Before revision:  The mathematical tractability of the model allows for the analytical computation of the epidemic threshold, thus extending to structured populations some primary features of the critical properties of mean-field models. Overall, the model is found in remarkable agreement with numerical simulations .
After revision:  The mathematical tractability of the model allows for the analytical computation of the epidemic threshold, thus extending to structured populations some primary features of the critical properties of mean-field model, the possibility of a bi-stable region is extended to structured populations .