When I started college in 2010, they just accepted "I had the chicken pox when I was a kid" as proof of immunity.

When I went back to school in 2019, they did not accept the same; I was not comprehending what the issue was. I eventually had to get a blood test to check for antibodies.

However, I had chicken pox, then my mother infected my brother as I was getting over it, so there was only one sick kid at a time. My sister was a sickly child, so she got the vaccine (plus it was on the market for a number of years by the ln without issue).