Within-household vs between-household transmission dynamics
S: — | I: — | R: — | Households infected: —
In household epidemic models, transmission is two-level: fast within-household spread (β_w ≫ β_b) and slow between-household spread. The household reproduction number R_H = R_0 · S̄_H/n_H determines epidemic fate, where S̄_H is the expected susceptibles infected per household generation. Even with R_global > 1, within-household clusters can exhaust local susceptibles, creating partial herd immunity.