Community Immunity Threshold Calculator

Estimate the vaccination or immunity threshold needed to reduce sustained spread based on the reproduction number (R₀) and vaccine effectiveness.

Higher R₀ means a more transmissible disease.
Use protection against transmission or infection when possible.
Approximate share already protected or immune.
Used to estimate how many people may still need protection.
Real-world programs often plan above the theoretical minimum.
Rounded targets are easier to communicate.
How we calculate

The classic threshold is based on the formula 1 − (1 / R₀). We then adjust that estimate by vaccine effectiveness and subtract existing immunity already present in the population.