Skip to content
ENExplore Calculators

Herd Immunity Threshold Calculator

Work out herd immunity threshold instantly with clear inputs, formula shown and shareable results.

About Herd Immunity Threshold Calculator

Applies the classic threshold of one minus the reciprocal of R0 and divides it by vaccine efficacy to give the coverage required.

Formula

Herd immunity threshold

HIT = 1 - 1/R0; required vaccination coverage = HIT / vaccine efficacy

Worked example

With the default values below, Herd Immunity Threshold Calculator returns Vaccination coverage required of 100.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Basic reproduction numberaccepts 1.01–25
12
Vaccine efficacy against infectionaccepts 10–100
90

Results

Vaccination coverage required
100.00%
Herd immunity threshold
91.67%
Feasibility
Threshold not achievable by vaccination alone at this efficacy
Susceptible share the population can carry
8.33%

Step by step

  1. 1Values used
  2. 2Herd immunity threshold
  3. 3Vaccination coverage required= 100.00
  4. 4Herd immunity threshold= 91.67
  5. 5Feasibility= Threshold not achievable by vaccination alone at this efficacy
  6. 6Susceptible share the population can carry= 8.33

Assumptions and limits

  • The result is derived only from the 2 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 2 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 does measles need such high coverage?

With R0 around 12 to 18 the threshold is 92 to 95%, which leaves almost no room for imperfect efficacy or uptake.

Does the simple formula always hold?

It assumes random mixing; clustered susceptibility means outbreaks can occur even above the nominal threshold.

Related Calculators

Herd Immunity Threshold Calculator | Calcrivo