SIS Epidemic on Networks

Susceptible-Infected-Susceptible dynamics on random and scale-free networks. Below R₀ = 1 the epidemic dies out; above it persists.

Network

Epidemic

State

Infected (I)0
Susceptible (S)0
R₀ = β⟨k⟩/γ—
Epidemic?—

R₀ > 1 → endemic equilibrium. For scale-free: threshold → 0 (Pastor-Satorras 2001)