Basic reproduction number R₀
3.0
Vaccination fraction p
0.00
Recovery rate γ
0.10
R₀: 3.0
HIT: 66.7%
Vax: 0.0%
S: 100.0%
I: 0.1%
R: 0.0%
HIT: 66.7%
Vax: 0.0%
S: 100.0%
I: 0.1%
R: 0.0%
Herd Immunity Threshold
HIT = 1 − 1/R₀
When vaccinated fraction p ≥ HIT, the effective R = R₀(1−p) < 1 and the epidemic cannot grow.
Measles (R₀≈15): HIT ≈ 93%
COVID Delta (R₀≈6): HIT ≈ 83%
Flu (R₀≈2): HIT ≈ 50%
HIT = 1 − 1/R₀
When vaccinated fraction p ≥ HIT, the effective R = R₀(1−p) < 1 and the epidemic cannot grow.
Measles (R₀≈15): HIT ≈ 93%
COVID Delta (R₀≈6): HIT ≈ 83%
Flu (R₀≈2): HIT ≈ 50%