SIR model on a 2D lattice — watch wave fronts propagate and herd immunity emerge
The SIR model divides a population into Susceptible, Infected, and Recovered compartments. On a spatial lattice, local transmission creates visible wave fronts, while the long-range spread parameter models air travel — seeding new outbreaks far from the front. The basic reproduction number R₀ = β/γ determines epidemic fate: if R₀ > 1, the epidemic grows. Vaccination removes susceptibles from the pool, lowering effective R.
SIR modelepidemiologypercolationherd immunity