Some people just have an exceptionally strong innate immune system, and that manages to kill things off before they manage to become established. Does being vacin ated make this kind of transient infection or early killing off of the virus more likely? Yes, probably it does. There's been a lot of media focus on breakthrough infections, that is, people getting infected with covid even though they've been vaccinated. But i think it creates perception that vaccines are only any good at protecting against severe disease - when in fact we're still very effective at preventing people from being infected in the first place. It's just they're not as effective as we originally thought they would be.