January 27, 2022 by Dr Kathryn Hackman

How to answer when your child asks “How do vaccines work?”

By now you’ve probably explained to your child that they will need a vaccine and why. Now they want a science lesson! This is such a great one and super fun to explain to young kids. Any fight analogy is going to work well for 3 – 7 year olds! 

Here’s how I explained the answer to my children.

Your body is already very clever at fighting diseases.
It fights them every day and you don’t even know about it.
But some diseases can make you really sick, and others are good at hiding, so your body can’t fight them.
Vaccines make it easier for your body to find and fight disease.

How they work is they show your body a little part of what the disease looks like.
That way your body can make an army to fight that part of the disease.
Then, if you get the real disease, your body already knows what it looks like, and has an army ready to attack!

Because the vaccine only gives you part of the disease, not the whole thing, it won’t make you sick.
It just helps your body get ready to fight the real disease, if you get it.

Then, even if you get the disease, you might not even know about it, because your body will just fight it for you.

As my kids got older and wanted more detail, I explained that “the army is actually your infection fighting cells.
Your body can build a bigger army, and quicker, every time it sees the vaccine, or the disease.”

With Covid-19 requiring multiple doses of vaccine, you may also want to add:

Some vaccines you need only once and your body remembers what to do, but mostly the army that you made at the start gets smaller.
To build it up again, your body needs another dose of the vaccine – to see the bad guy again and remember what it looks like.
That way it can build an even bigger army which works even better, if you get the disease.

For younger kids (or even older kids – my 6 year old still loves this part) I do a role play.
Here’s the scene:

The bad guy disease comes along, in disguise, and says “la la la, nothing to see here.”
But after the vaccine your body says – “hang on a minute, I SEE you!!!”
And your body calls in its special army and kills off all the bad guys!
And then you don’t get sick. 

For older kids, or if you want a little more detail, there is a good outline of immunity here.

AboutDr Kathryn Hackman
Founder of the Courageous Kids children's storybook app, is a practicing clinician and loving mother of two beautiful boys.

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