Epidemic spreading and immunization with identical infectivity

In this paper, a susceptible-infected-susceptible (SIS) model with identical infectivity, where each node is assigned with the same capability of active contacts, $A$, at each time step, is presented. We found that on scale-free networks, the density of the infected nodes shows the existence of threshold, whose value equals 1/A, both demonstrated by analysis and numerical simulation. The infected population grows in an exponential form and follows hierarchical dynamics, indicating that once the highly connected hubs are reached, the infection pervades almost the whole network in a progressive cascade. In addition, the effects of random, proportional, and targeted immunization for this model are investigated. Based on the current model and for heterogenous networks, the targeted strategy performs best, while the random strategy is much more efficient than in the standard SIS model. The present results could be of practical importance in the setup of dynamic control strategies.