Description of the Interactive Tool
This model demonstrates the spread of a virus through a network. Each node may be in one of three states: susceptible, infected, or resistant (the so-called SIR model).
Each time step (tick), each infected node (coloured in red) can infect all of its neighbours. Susceptible neighbours (coloured in green) will be infected with a probability given by the VIRUS-SPREAD-CHANCE slider. Resistant nodes (coloured in grey) cannot be infected. They behave as if they were vaccinated.
Infected nodes are not immediately aware that they are infected. Only every so often (determined by the VIRUS-CHECK-FREQUENCY slider) do the nodes check whether they are infected by a virus. When the virus has been detected, there is a probability that the virus will be removed (determined by the RECOVERY-CHANCE slider).
If a node does recover, there is some probability that it will become resistant to this virus in the future (given by the GAIN-RESISTANCE-CHANCE slider).
When a node becomes resistant, the links between it and its neighbours are darkened, since they are no longer possible vectors for spreading the virus.

Points of Strength
This model is valuable to show how “Chemical Waves” spread in a Complex System that can be represented as a network. Chemical waves might be generated by viruses, fads in society, species that colonize a new environment, fire, etc.