Frequently Asked Questions
What is the herd immunity threshold?
It is the share of a population that must be immune so each infection causes fewer than one new infection, calculated as one minus the reciprocal of the reproduction number.
Why is required coverage higher than the threshold?
No vaccine is perfectly effective, so coverage must exceed the threshold by dividing it by the vaccine efficacy.
Why do different diseases require different vaccination thresholds for herd immunity?
The herd immunity threshold depends on R₀, the basic reproduction number. Measles has an R₀ of 12–18, requiring 92–95% immunity - one of the highest thresholds of any vaccine-preventable disease. Polio requires roughly 80–85%, seasonal influenza about 33–44%. A more contagious pathogen spreads to more people per case, so a larger immune fraction is needed to break transmission chains. Waning immunity, vaccine hesitancy, and uneven population mixing can push the effective threshold even higher than the theoretical value.
Provided by AllCalculators.io
Free online calculators for everyday. No registration required.
General information only. Not medical advice.
Health & Medical Disclaimer: General information only. Not medical advice.
This calculator provides general health information only and is not medical advice. Results do not replace professional medical evaluation or diagnosis. Consult a licensed healthcare provider before making health decisions. Always seek immediate medical attention for emergencies.