FWIW, I flew with someone who apparently had COVID (asymptotic at the time) shortly after my second shot. Spent 4 days together, mask less in the cockpit..... He became symptomatic after the trip. I got NOTHING..... I also tested negative after 6 days from last contact. Maybe low viral load while in contact with him or maybe the vaccine worked..... Who knows? If it was the vaccine, perhaps close contact doesn’t matter???