One of my sons got his Moderna booster in June. He was to leave for Japan to start teaching a month later, and the Japanese government required that he be tested 4 days before leaving. He was positive.
A lot of good that did him to get the booster.
Luckily, he was able to fly with a second group 3 weeks later but we were all agonizing until the second test because we know people who have inexplicably still tested positive a couple of weeks later.