Activity 1: How Vaccines Work

PDF versions of Activity 1: How Vaccines Work are available in English and Spanish.

Objectives: Students will understand on a very basic level how antibodies of the immune system work and what memory is. They will learn how vaccines work by using weakened or killed germs to trigger the body’s immune response.

Materials: thick foam or cardboard (for antibody and germ cut-outs), sticky notes


Have you all ever heard of a vaccine? Yes? Do you know what they do? (Hopefully they’ll respond that vaccines keep you from getting sick. If not, explain this.) That’s right, vaccines are great because they help us stay healthy! But have you ever thought about how they work?

Well, when a germ gets into your body, three things happen:

1. First, you get sick because of the damage the germ is doing to your body.

2. Meanwhile, antibodies, which are like puzzle pieces that your body makes, find a way to match to the germ making you sick in order to kill it.

3. Once your antibodies figure out how to match and kill the germ, your body learns to recognize that germ so that the next time it enters your body, you will be immune to it, meaning that it can’t make you sick. This is called memory – the antibodies in your body actually remember the germs that have made you sick before so that they can kill the germs right away next time.

So, back to vaccines. Vaccines take advantage of something your body already knows how to do, which is remembering germs it has seen before.  They work by putting a weakened form of a germ into your body. The germ is weak because it has been changed in a lab by scientists, so it can’t make you sick like it normally would. But your body still learns to remember it! Once your body recognizes and remembers a germ, even if it is a weakened germ, that germ can’t make you sick the next time it gets into your body. This is how vaccines protect you from getting sick!


  • Several (1-4) kids are “antibodies” inside a room which is the “body”, each holding a cardboard cutout. The cutout is the antigen binding site.
  • One germ, representing the chicken pox virus, holding the match to the cutout (its “antigen”) walks into the room and “does damage” to the body by peeling sticky notes off of the wall.
  • The antibodies try to match their cutout to the one on the germ (antibody matching antigen), one at a time. One antibody will have the correct match.
  • When the correct antibody matches the germ, the germ has to stop peeling off sticky notes. The entire time the germ is peeling off post it notes and the antibody hasn’t recognized it yet, the body is “getting sick”. Once the correct antibody matches their cutout to the germ, the body begins to recover.
  • Then, the activity is repeated, everyone holding the same cutouts and with the same chicken pox germ. This time, the correct antibody should recognize it immediately and bind to it, stopping the germ from peeling off any sticky notes and therefore stopping the body from getting sick at all because the response is so fast. This represents memory.
  • The activity is repeated a third time but with a different germ – the measles germ. This time, though, the germ is introduced into the body as a vaccine, and is in a weakened form. The measles germ is shown to be weakened by having their hands tied behind their back.
  • The antibodies must again figure out which one is the correct match for the measles – it will be a different match than the first, chicken pox, one. However, this time, the germ cannot do any damage by peeling sticky notes off the wall since it is in its weakened form.
  • Once the correct antibody binds to the germ, it has learned to recognize that germ. Explain to the kids that the body has learned memory but without getting sick by being introduced to a weakened form of the same germ in a vaccine.

Post-activity discussion questions:

  • How do your body’s antibodies recognize foreign germs?
  • Why can’t a germ make you sick the second time it gets in your body?
  • Why can’t germs in a vaccine make you sick? How do they protect you?