Link. Immense details on immune studies of these 2021 healthy young volunteers. About 1/5 NEVER were PCR positive despite being infected; the innate immune system worked fast. (Most people who say they never got COVID are presumed to be like this. They got COVID (virus), killed it, never noticed).

“authors were also able to find a blood marker that could distinguish the sustained-infection group from those where the virus didn’t get a chance to establish itself … HLA-DQA2, whose function is not really clear yet.”