Saved on this device

Follow your curiosity

What discovery has been shared with you?

FACTREE gives you something interesting to discover every day — and something worth talking about together.

Start with one fact. Explore it, go deeper, then follow whichever branch catches your imagination.

Choose subjects for a surprise

Exploring any topic

Begin your discovery

Your next discovery is one click away.

Choose one or more subjects above, or leave Any Topic selected and let curiosity decide.

Biology

Vaccine-Induced Immunity and Herd Immunity Thresholds

Quick fact

For measles, one of the most contagious diseases known, about 95% of the population must be immune to stop its spread. That’s why even a small drop in vaccination rates can cause outbreaks.

Why this is interesting

You’ve probably heard that vaccines protect not just you, but also your community. But how does a vaccinated person actually shield someone who hasn’t been vaccinated? The answer lies in a surprisingly simple mathematical threshold.