I'm going to speculate that many of the longer term chronic and/or new effects of COVID infection will eventually be linked to rare diseases that were suspected of having a link to some unknown infectious disease. For example, Kawasaki's disease
Kawasaki Syndrome | CDC is of unknown etiology. COVID causes MIS-C
COVID-19 and Your Health which is somewhat similar. Now some researchers are storing to look at both in parallel
New findings in COVID-related kids' syndrome, Kawasaki disease. It may well turn out that secondary effects from initially asymptomatic or clinically insignificant infections (maybe from other viruses, including the coronaviruses that cause the common cold), have always been with us, but that this singular event where we can identify a novel agent and test for it in both symptomatic and asymptomatic patients (because now we have a target to look for) might be an important advance in understanding other patients with ill-defined debilitating chronic malaise and fatigue
Will Long COVID Change the Game for Autoimmune Diseases, too? Part 1 – Autoimmune Connect