Anderson-May 1985: critical-immune-fraction p_c = 1 − 1/R_0 to halt transmission. Measles R_0 ~12-18 → p_c ~92-95%. Influenza R_0 ~1.3-1.8 → p_c ~25-45%. Heterogeneous-mixing reduces effective threshold; antigenic-drift erodes it (flu).…
Anderson-May 1985: critical-immune-fraction p_c = 1 − 1/R_0 to halt transmission. Measles R_0 ~12-18 → p_c ~92-95%. Influenza R_0 ~1.3-1.8 → p_c ~25-45%. Heterogeneous-mixing reduces effective threshold; antigenic-drift erodes it (flu).…