THe study Ganesha posted seems oddly structured. They say that 81% of blood samples from patients with a history of COVID-19, the samples had the antibody.... In participants with no history of COVID-19.
So they contrast people w Covid and people without Covid. But they don't contrast people w Long-Haulers and people who (had Covid but) didn't have Long-Haulers. Which would be a study worth doing. If it caused LH, it would show up in LHers and not in people who didn't get LH.