Months? How long has Omicron been around? 2 months. Vaccination actually was fairly protective FROM INFECTION before Omicron. Even with Omicron it doesn't provide no protection against infection but there are lots of breakthroughs.No vaccination doesn't prevent covid. It prevents severe outcomes from it. You're months behind on your info.
But anyway anyone who was vaccinated before Omicron and took precautions since is not necessarily "all going to get covid" presuming they didn't already have it. I upped precautions because I knew whatever info we had going into the holidays was probably going to be complete garbage, and we'd have to wait for the fog of the holidays to pass before much of anything would be known (re Omicron). Finding antibodies in someone's blood does not mean they EVER had covid, as vaccines produce antibodies as well.