Have you 'herd'about herd immunity? How vaccines work to keep us healthy

This activity links with Grade 8 Science: Life Processes are performed at the cellular level. Modified from 2013 Science Ambassador Workshop Lesson Plan


What you need

  • A group of friends or your class at school
  • Small red, green and blue items e.g. jelly beans, pieces of paper (in a bag). Include 2 red items (representing people with a communicable disease like the flu), and equal numbers of green (representing vaccinated people) and blue (representing unvaccinated people)
  • Soft squishy balls – small and soft enough to be thrown at students without hurting anyone – one ball for every two people playing

What to do

  1. Have each person randomly pick an item from the bag. Explain that the students with a red item have the flu and can spread it to other people; students with green items have been immunised and are protected against infection with the flu; and students with blue items have not been vaccinated and are not protected.
  2. The two people with red items should sit down, and all the others stand up.
  3. The students with red items get a squishy ball each. When the game starts, they can throw the ball at anyone who is standing. They should try to hit the standing students in the torso (front or back). Students with green items are protected and so can use their hands to deflect the balls. Students with blue items are not protected and must keep their hands by their sides. Unvaccinated students (blue) who get hit on the torso must sit down. They are now sick and get a squishy ball to throw. Vaccinated students (green) hit on the torso stay standing.
  4. After 4 throws per sick person, stop and see how many people are sick (sitting down).
  5. Now try the whole thing again but this time have all the well students with green items (vaccinated and protected from the flu) circle around the well students with blue items (not vaccinated and so not protected from the flu) and have the original two sick students (with red items) throw the squishy balls.
  6. Allow the same number of throws, and see if this makes a difference to the numbers of students who become sick.

What's going on?

In the second part of the activity the unvaccinated students (inside the vaccinated student circle) are much harder to hit with the squishy balls, showing that the vaccinated students protect the unvaccinated ones. This is how herd immunity works.

What do you think would happen if more students were green (vaccinated)? Once a critical number of people are vaccinated it becomes almost impossible for an unvaccinated student to get infected. What if more students were not vaccinated (blue items)?

Have a discussion about the reasons why people may not be vaccinated – medical exemptions (e.g. allergic reactions to vaccine, have an acute illness, compromised immune system, too young to be immunised yet), religious exemptions, philosophical exemptions. 


Meet scientist Fiona Brinkman

Fiona Brinkman is a professor in the Department of Molecular Biology and Biochemistry at Simon Fraser University. 

Dr. Brinkman's research focuses on understanding microbes; not only how they evolve but also how we can better develop new vaccines, drugs and diagnostics to combat infectious diseases. 

Involved in multiple Genome Canada projects, she was recognised as one of Thomson Reuters “World’s Most Influential Scientific Minds: 2014”.