Did you know that vaccine derives from the Latin for cow? This is because the first vaccine was derived from "cowpox" to immunize humans against smallpox. Humans were treated with the cow (vacca) antibodies and they didn't get smallpox*.
Vaccine, however, has nothing to do with vacation, which I am now on.
(Nota bene: not all fascinating facts will be about bacteria, but bacteria have been occupying my mind lately due to what I thought was the return of a hated sinus infection.)
*(Funny I originally typed "small box" there. Funny, that.)