SIR

β = infection rate per contact. γ = recovery rate. Ideal well-mixed: R₀ = β/γ. Network: replaced by network-based R₀.

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Percolation threshold

Above critical infection rate, epidemic infects fraction of network. Below: dies out.

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Scale-free danger

Scale-free networks: no epidemic threshold! Any β > 0 → macroscopic outbreak. Due to high-degree hubs.

Targeted vaccination

Vaccinating high-degree nodes disproportionately effective. Extension of degree-centrality importance.