A very nice walkthrough of the basics of vacination and the spread of diseases. The walkthrough has simple and straightforward 2D simulation to demonstrate the effects of every component relevant to the spread of disease, such as infection rate and infection susceptibility. It makes it visible how a high vaccination rate makes the spread of diseases near impossible, and in turn helps all unvaccinated persons.

The basis of his simulations are networks: nodes have various kinds of relationships which can be perturbed by chance or other properties. Thanks Kevin Simler!