Rotavirus immunity is partial. You only need to come in contact with a strain too different from whatever your vaccine or childhood exposure was and you’ll catch it again.

I got the vaccine as a child, and yet I caught it in my early 30s for the first time after moving to another country. Have you seen The Exorcist? I didn’t know projectile vomit was a thing for real until then. I also didn’t know about projectile diarrhoea. I wish I was still ignorant of these things