Explaining microbiology and modern medicine to someone whose medical science hadn't progressed beyond 'insert frog in mouth' was not exactly high on Julian's list of things he'd like to do today. Oh well. Maybe he can get away with a simple explanation.

"Vaccinations are medicines that are specifically created to help your immune system--which is what naturally fights off infection--develop resistance to the illnesses that the vaccinations are for. So when you start getting sick, your body already knows how to fight it, and you don't actually show symptoms."