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[–><!–>Just how many? To let you discover for yourself, we simulated an outbreak of a hypothetical disease, about as contagious as the flu. (A lot less contagious than measles.)–><!–>
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[–><!–>We’d like you to contain it. But first, some basics:–><!–>
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–><!–>Here’s a sick person in a population with no protection against the disease.–><!–>–><!–>
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–><!–>Soon, almost everyone has been infected.–><!–>–><!–>
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[–>Chance of an outbreak growing out of control for a less contagious disease
100% chance
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[–>Chance of an outbreak growing out of control for a less contagious disease …
100% chance
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[!–>… and for a more contagious disease
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50% Vaccinated
75% Vaccinated
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[–><!–>For the most part, the 75 percent district is protected, while the 50 percent district is overrun, even though they sit right next to each other. Herd immunity operates at a local level, and the average vaccination rate for a broad region can mask smaller communities at risk.–><!–>
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[–><!–>The simulated world you saw above mirrors a real-world problem: There are increasingly many parts of the U.S. where skepticism of vaccines has gained momentum and childhood vaccination rates have fallen.–><!–>
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[–><!–>And measles is far more contagious than the disease we simulated — because of space constraints, we could not even simulate it in this form. It’s so contagious that a vaccination rate of 50 percent or even 75 percent won’t contain an outbreak.–><!–>
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[–><!–>Epidemiologists estimate the contagiousness of an infectious disease with a “basic reproductive number,” or R0 — how many people a sick person infects, in a community with no protection.–><!–>
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[–><!–>A disease can grow out of control if an infected person infects more than one other person, on average. A person with the flu can infect one to two others — an R0 between 1 and 2.–><!–>
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| Disease | Contagiousness (Est. R0) |
|---|---|
| Measles | |
| Whooping cough | |
| Covid (Omicron) | |
| Chickenpox | |
| Polio | |
| Covid (Delta) | |
| Flu (1918) | |
| Seasonal flu |
