Yes, it’s super interesting. The reason the word ‘vaccine’ derives from the Latin ‘vacca’ (cow) was because we observed that people who contracted the cowpox gained some protection from smallpox. We investigated that connection, did a bunch of testing and research (which included early scientists infecting themselves on purpose in some rather gross ways), and developed the theory of vaccines.

The history of early modern medicine is very cool.

Same, I get it a couple of times a year, and it's only ever extremely severe. I would love to know the secret.