What's the Risk?

"1 in 10,000" and "1 in a million" both just sound rare, even though one is a hundred times the other. This tool turns risk numbers into squares you can see and compare, a vaccine against the disease it prevents, or either one against everyday risks like a car crash or a lightning strike. Pick a comparison below, or build your own.

Before you compare: a few things to know

The disease side shows what could happen if you get infected. The vaccine side shows what could happen if you get vaccinated. These aren't equally likely.
Your chance of catching a disease varies a lot. It can depend on where you live, what's going around, whether there's an outbreak nearby, whether and where you travel, and how many people around you are vaccinated. There's no single number that fits everyone, so we don't include one here.
Where infection risk is low today, vaccination is a big part of why. For measles, about 90% of people caught it by adulthood before the vaccine existed. Low risk is something communities built, and it goes back up as vaccination rates fall.
Some diseases spread very easily once you're exposed. Measles, for example, infects about 90% of unprotected people who are exposed. Being unlikely to run into a disease and being unlikely to get sick from it are two different things.
Vaccines aren't perfect. A chance of illness remains after vaccination, but in the case of the measles vaccine, for example, protection is extremely strong and durable: 97% after two doses and generally lifelong. Hundreds of millions of doses have been administered over 60 years, so protection estimates are backed by decades of data.
These numbers are averages for the age group shown, not a prediction for one person. Your own risk depends on your age, health, and situation.

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Serious outcome Mild or temporary outcome

How to read this

The gray area represents 100,000 people in the relevant population, shown by the color-coded age band atop each chart. Each colored square is sized so its area equals the number affected, so very rare risks appear as tiny specks and common outcomes as larger blocks. Comparisons are most reliable within the same population. When two charts cover different age groups or timeframes, treat the comparison as a rough sense of scale rather than a precise apples-to-apples number. Hover or tap any square for details and a link to the data source.