Activity 2: Shooting Down the FLU!

PDF versions of Activity 2: Shooting Down the FLU! are available in English and Spanish.

Objectives: Many students will be familiar with getting a flu shot, so this activity uses it as an example of the crossroads of evolution and medicine. Kids will use apply knowledge of how the immune system works to a specific example – the flu. The flu is also a unique example in that it requires a new vaccine every year, which can be explained by evolution of the virus.

Materials: Dixie cups (NOT clear), small colored pom-poms or beads


You guys have all heard of flu shots, right? I bet a lot of you have had to get them before. But do you know how they work?

Well, the flu is a type of virus, which is a germ. A virus is a germ that gets into your body and then makes lots of copies of itself, making you sick.

Does anyone know how your body protects itself from getting sick? Your body uses something called the immune system to fight germs that could make you sick. The immune system is smart, and learns how to recognize the germs. When your body has learnt to recognize and destroy a germ, we say it has “built immunity” to it. When you are immune to a germ, it can’t make you sick!

So how does any of this have to do with flu shots? When you get a flu shot, what it does is make your body immune to the flu. The shot actually puts part of the flu virus into your body! By putting pieces of the flu virus into your body but not all of it, your body learns to recognize and destroy the virus and that way you become immune to the flu, but without getting sick.

So if the flu shot makes you immune to the flu, how come you have to get a new shot every year? Does anyone know? It’s because the flu virus evolves – meaning changes – from year to year. Because of that, there are many types of the flu that are around all the time. We call these types “strains”. Scientists have to predict what will be the strain that will make people sick every year, and then make the right kind of vaccine for that strain of flu.

Scientists can guess how the strain of next year will look like by studying the strains that are around this year. Next year’s strain will necessarily come from this year’s. It will look like whatever is most common this year because there will be more copies of that. The shot for next year will have the bits of these year’s viruses that are more abundant.

So in this activity YOU are the scientists, and you have to choose what to put in the vaccine to protect the most people from the flu this year!


  • Have lots of colored pom-poms laid out on the table. One color needs to be obviously predominant (for example, 20 green pom-poms, one purple, one blue and two pink). These represent this year’s strains of the flu.
  • Explain to the kids that it is best to be vaccinated against the most common flu strain of the year. Based on that, ask them to choose which color strain do they want the vaccine for. Have them pick up a pom-pom of that color (the predominant one) and hold onto it – that is the vaccine they’ve received. Explain that they are now immune to that strain, and were smart to choose the most common strain.
  • Then, once they have chosen the vaccine (single color) that matches the predominant strain (the predominant color in the mixed pile), they will move on to another set of five cups, but that are upside down. These cups are each covering one pom-pom, and represent next year’s virus strains. Ensure that the vaccine’s color is the most frequent, but it should not be the only color represented (ex – 3 of the predominant color and 2 random colors). There has to be a diversity of strains.
  • Have a kid pick up one of the cups covering a flu strain. If they uncover the same color as the predominant strain that year and of the vaccine they received, they don’t get the flu. This is the most likely situation. But, if they uncover a color that is not that year’s strain, they “get the flu” because they received only the vaccine for that year’s strain.
  • Have them do this last part several times, mixing the cups around each time, to show the probability of them getting the flu if they received the vaccine.

Post-activity discussion questions:

  • How many of you got the flu this year, and how many of you didn’t? Why do you think some of you got the flu even though you got a flu shot?
  • Why does the flu shot actually introduce pieces of the flu into your body – wouldn’t that make you sick?
  • Why do you think the virus changes from year to year? (wait for responses). Let’s see: Who do you think is going to make more copies of itself (this is how viruses reproduce), the most common virus strain that is unsuccessful in people that got the vaccine, or the strains for which no one had immunity? That’s right; the most successful viruses will be those that are not destroyed by our immune system, those for which we have not built any immunity. That is why the flu vaccine needs to be different every year! Thanks to the vaccine, we can destroy some strains, but the strains that escape our immune system will generate copies of themselves and become next year’s flu strains. So you’ll have to get a shot for a different flu strain next year.