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Science

Vaccination and Herd Immunity

Overview

Students explore how vaccines work at the population level, discovering how herd immunity protects vulnerable individuals and why vaccination rates matter for public health.

Learning Objective
Students understand the mathematics of herd immunity and can evaluate vaccination policy using epidemiological concepts.

Resources needed

  • None

Lesson stages

0 / 7 done
  1. 1 Recap: vaccines create immunity without causing disease. But why does it matter if most people — not everyone — are vaccinated?
  2. 2 Introduce R0 (basic reproduction number): the average number of people one infected person will infect in a fully susceptible population. Measles R0 is approximately 15; flu is approximately 1.3.
  3. 3 Introduce herd immunity threshold: the proportion of a population that must be immune to prevent an epidemic. Formula: 1 minus 1/R0.
  4. 4 Calculate: for measles (R0 = 15), herd immunity threshold = 1 minus 1/15 = approximately 93%. Why does measles require such high vaccination rates?
  5. 5 Discuss who benefits from herd immunity: newborns too young to vaccinate, immunocompromised individuals who cannot receive vaccines, and those in whom vaccination fails.
  6. 6 Simulate disease spread: a class activity — most students are vaccinated (stand), a few are not (sit). An infected student attempts to infect others. How does vaccination rate affect spread?
  7. 7 Discuss vaccine hesitancy: what causes it, how to address it, and the consequences of declining vaccination rates.

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Variations

  • Plot the effect of different R0 values on herd immunity thresholds — why are some diseases harder to control?
  • Discuss the 1998 MMR-autism claim: how it was made, why it was wrong, and the harm it caused.
  • Compare vaccination strategies: mass vaccination campaigns vs routine childhood immunisation.
More information

Teach: R0, herd immunity, threshold, epidemic, susceptible, immune, vaccination rate. The simulation activity is the most powerful teaching tool — students directly experience how vaccination rate affects disease spread.

Focus on the concept of R0 and the herd immunity threshold calculation before introducing the ethical and policy dimensions.

Can students calculate the herd immunity threshold for a disease given its R0 value? Can they explain why achieving herd immunity requires a higher vaccination rate for diseases with higher R0 values?

No resources needed. The simulation requires only students willing to stand and sit. Calculations require only arithmetic.

Students often think that if most people are vaccinated, unvaccinated people are fully protected by herd immunity. Herd immunity reduces but does not eliminate the risk for unvaccinated individuals — those in the group are still more vulnerable than vaccinated individuals.

Herd immunity is one of the most important concepts in public health. Understanding the mathematics explains why measles requires near-universal vaccination, why flu vaccination is only partially effective, and why vaccine hesitancy has population-level consequences.

Activity details
Secondary Medium 25 minutes no prep Whole Class, Small Group Indoor & Outdoor
Topics
Vaccination Herd Immunity Epidemiology