Correlation may not equal causation, but correlation does define syndromes. In medicine, a "syndrome" is any collection of findings that tend to occur together

Correlation may not equal causation, but correlation does define syndromes. In medicine, a "syndrome" is any collection of findings that tend to occur together. A syndromic label says nothing about how or why the findings occur together, only that they do. As syndromes become better understood, they can morph into a disease. For example, swollen lymph nodes in gay men was a syndrome in 1981, but as knowledge evolved, we came to know it as AIDS and then HIV. So "long covid" is definitely a syndrome. Hopefully medical science will someday learn enough to know whether it is a disease or not.