Scenario: With 70% vaccination coverage, a 90% effective vaccine, and R₀ = 5.0, herd immunity requires 80% of the population to be immune. Each infected person still infects ~1.5 others on average, so the disease will continue to spread.
Tip: Herd immunity threshold = 1 − 1/R₀. Try measles (R₀ ≈ 15) with 90% coverage, or influenza (R₀ ≈ 2.5) with 60%. Press R to reset to default.