Leon actually smiles again at the enthusiasm. It's not surprising, but it a reminder of just how exciting something that he's taken for granted basically his whole life really is.

"Yeah. They're pretty great. I don't remember when they were invented, but by the time I'm from? There's a few diseases that used to be way too common that now almost no one gets anymore. Outbreaks can still happen, but they're much easier to control if everyone who can be vaccinated is."