Vaccine Coverage Requirement Calculator

Work out vaccine coverage requirement instantly with clear inputs, formula shown and shareable results.

About Vaccine Coverage Requirement Calculator

Works out the coverage needed to reach the herd immunity threshold given vaccine efficacy, and shows the effective reproduction number at current coverage.

Formula

Coverage requirement

Required coverage = (1 - 1/R0) / vaccine efficacy; effective immunity = coverage x efficacy; Rt = R0 x (1 - effective immunity)

Worked example

With the default values below, Vaccine Coverage Requirement Calculator returns Coverage required of 98.04%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Basic reproduction numberaccepts 1.01–25: 6
Vaccine efficacyaccepts 10–100: 85
Current coverageaccepts 0–100: 70

Results

Coverage required: 98.04%
Additional coverage needed: 28.04%
Effective population immunity now: 59.50%
Rt at current coverage: 2.430

Step by step

1Values used
2Coverage requirement
3Coverage required= 98.04
4Additional coverage needed= 28.04
5Effective population immunity now= 59.50
6Rt at current coverage= 2.430

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is effective immunity lower than coverage?

An imperfect vaccine protects only a share of those vaccinated, so immunity equals coverage times efficacy.

Does timing matter?

Yes. Waning immunity and birth cohorts continually add susceptibles, which is why coverage must be sustained.