Calculator Inputs
Threshold Visualization
The graph compares the theoretical immunity threshold and coverage requirement across changing R₀ values.
Example Data Table
| R₀ | Vaccine Efficacy % | Herd Threshold % | Required Coverage % |
|---|---|---|---|
| 2 | 95 | 50.00 | 52.63 |
| 3 | 90 | 66.67 | 74.07 |
| 5 | 85 | 80.00 | 94.12 |
| 8 | 92 | 87.50 | 95.11 |
Formula Used
H = 1 − (1 / R₀)
C = H / E
I = (Vaccination Coverage × Vaccine Efficacy) + Natural Immunity
The herd immunity threshold estimates the immune proportion needed to reduce sustained spread. The required vaccination coverage rises when vaccine efficacy decreases. This page also compares current effective immunity with the calculated threshold.
How to Use This Calculator
- Enter the basic reproduction number, or R₀.
- Provide vaccine efficacy as a percentage value.
- Enter total population for people-based estimates.
- Fill current vaccination coverage percentage.
- Add estimated natural immunity percentage.
- Choose decimal precision for result formatting.
- Click Calculate Threshold to display results.
- Review the graph, metrics, and example table.
- Export the result as CSV or PDF.
This calculator supports educational scenario analysis. It should not replace official epidemiological modeling or clinical guidance.
Frequently Asked Questions
1. What does herd immunity threshold mean?
It estimates the immune share needed to reduce ongoing disease spread. When immunity reaches this level, each case produces fewer new cases on average.
2. Why is R₀ important in this calculator?
R₀ describes how many people one infected person may infect in a fully susceptible population. Higher R₀ values create higher immunity thresholds.
3. Why does vaccine efficacy affect coverage requirements?
A vaccine that is less effective protects fewer vaccinated people. That means more overall coverage is needed to reach the same effective immunity level.
4. Does this calculator include natural immunity?
Yes. It lets you add an estimated naturally immune percentage. That value contributes to total effective immunity in the simplified model.
5. Can required coverage exceed 100 percent?
Yes, mathematically it can. That result means vaccination alone cannot reach the threshold under the chosen assumptions and parameters.
6. Is this tool suitable for real public health decisions?
It is best for education, planning exercises, and rough comparisons. Real decisions require updated surveillance data, expert models, and policy context.
7. What does additional vaccination needed show?
It estimates the extra share of the population that must be vaccinated, assuming the given efficacy, to close the remaining immunity gap.
8. Why export CSV and PDF results?
CSV files support spreadsheet analysis. PDF files help with quick sharing, documentation, and reporting of the chosen scenario and output values.