Why do you have to get vaccinated?

When you get an injection, like a vaccine, it has a special kind of medicine in it. This medicine has little pieces of a germ, like a virus or bacteria, that can make you sick. But the medicine makes these germ pieces weaker, so they can't actually make you sick.

When the medicine with the weak germ pieces gets injected into your body, your body see them and says "Uh oh, we've got some germs trying to get in!" Your body then sends out little soldiers called lymphocytes to attack them.

After they fight off the weak germ pieces from the injection, some of the lymphocytes remember what those germs looked like. These are called memory cells.

The memory cells are like your body's secret agents. They stay in your body, ready to fight them off even before you get sick if these same germs ever try to get in again. Isn’t the human body amazing?