Herd Immunity Threshold
Vaccination coverage, indirect protection, and outbreak prevention dynamics
Parameters
R₀ (basic reproduction number):
4.0
Vaccine coverage p:
60%
Vaccine efficacy ε:
95%
Simulate Outbreak
Herd Immunity Status
R₀
4.0
HIT (1-1/R₀)
75.0%
Effective coverage
57.0%
Effective R
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Outbreak will...
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Herd immunity threshold HIT = 1 − 1/R₀. Above it, outbreaks die out. Effective coverage = p × ε. Measles R₀≈15 needs 93% coverage.
Coverage vs threshold:
57%
HIT 75%