Simulator
Scale
R number
Practice
How contagious
Vaccinated
Physical distancing
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🔢
R₀
average number of people each sick person infects
📈
R > 1
outbreak grows
📉
R < 1
outbreak shrinks
🤧
Measles
R₀ about 12–18: very contagious
💉
Herd immunity
enough immune people to block spread
🔬
Epidemiologists
scientists who track diseases