This Demonstration compares the spread of an epidemic in random and scale-free networks of identical densities with and without inoculation of the most central 10% of the nodes. You can set the size of the network, the number of time periods, the contagiousness of the disease, and the probability of recovery within a time period. In both types of networks positions average four connections.

The simulation can be used to compare epidemic outcomes in random and scale-free networks. Two lessons can be drawn:

• Inoculation of the most central nodes has a greater effect in scale-free than in random networks because the former type is more centralized and skewed in the distribution of number of connections.

• In scale-free networks there is no critical value for whether or not the epidemic dies out.