How Do Vaccines Train Immune Cells?

Imagine your body is a castle with guards who wear blindfolds. When a bad guy like a virus attacks for the first time, the guards are confused and take a while to put on their armor. A vaccine is like showing the guards a picture of the bad guy before he arrives.

The vaccine gives your body a tiny piece of the germ or a weakened version of it. This piece acts as a model. Your immune cells look at this model and learn what it looks like.

Once they have seen the model, your body creates special soldiers called memory cells. These soldiers remember the germ forever. If the real germ ever tries to invade again, those memory soldiers wake up immediately. They know exactly how to defeat it before you even feel sick.