I have no doubt that such people exist, but they can't be that common, right? And to the extent they do exist, wouldn't their symptoms have generally been extremely mild? So you would expect most such individuals to not believe they've had COVID and to not have long-COVID, and therefore not to confound the results of this study.

In addition, it’s the immune response that likely leads to Covid organ damage so if an infection is interrupted so early as to not initiate an antibody response you’d expect any long covid effects to non-existent.

8.5 billion times a small percentage is still a pretty big number.

I'm not understanding the relevance. We are talking about the proportions of folks that fall into various buckets. The absolute values don't enter into this conversation.

I know quite a few people who believe that you can have long COVID without any initial symptoms, so it seems reasonable that there may be some people who got mild symptoms, believed it was COVID, and then have some ongoing symptoms that they attribute to that.

That is a very long and detailed paper, so apologies if I missed it, but I don't see any evidence of a "large population" of folks that clear the infection quickly enough to avoid triggering an antibody response. All I see from that paper, is that such people exist.

If you’re willing to take extended data table 1 at face value [0], then perhaps 1/2 to 1/3 of the exposed cohort is in this category. This is at least moderately consistent with other data suggesting that at least around 2/3 of the naive population will contract COVID and test positive on PCR is exposed.

In other words, the authors found a population that apparently did clear the infection this quickly, and they didn’t scour a particular large cohort to find these people.

[0] which you shouldn’t.