IIRC this idea is the origin of the word “vaccine” - from vache, French for “cow” - people used to intentionally get infected with cow pox 300 years ago, and it

IIRC this idea is the origin of the word “vaccine” - from vache, French for “cow” - people used to intentionally get infected with cow pox 300 years ago, and it would confer protection against smallpox. On phone so hard to check and link.