Chapter 10 part 2

Madam Pomfrey's potions are failing at Hogwarts. A new "Hogwarts Flu" is spreading,

and the wizarding version of antibiotics just isn't working. Here's the secret: the illness is a

hybrid, part bacteria and part virus. Antibiotics are designed to kill

bacteria, so they're useless against the viral half. Even worse,

Professor Snape was right. Overusing these potions makes the microbes evolve

and become resistant. So how do you fight it? Your own body has the answer.

Your immune system creates memory cells to remember the invader, letting you defeat

it faster next time. This is exactly how a "vaccine charm" would work.