SIS Epidemic — Heterogeneous Network

Scale-free network (BA model): epidemic threshold λ_c = ⟨k⟩/⟨k²⟩ → 0 as N→∞

Infection rate β: 0.3

Recovery rate μ: 0.5

Network size N: 60

m (edges/node): 2

Infected I: —

Susceptible S: —

Prevalence: —

λ=β/μ: —

⟨k⟩: —

Threshold λ_c: —

Nodes: green=susceptible, red=infected. Hubs (high degree) act as super-spreaders. For scale-free networks, epidemic threshold → 0 as N→∞ (Pastor-Satorras & Vespignani 2001).