We all assumed it was covid, but once antibody tests became widely available, we all went and got them - and none of us had antibodies. I actually got like three different antibody tests over the span of two months because I couldn't believe I hadn't had covid. All negative.
So maybe we just all caught a bad flu bug? It was pretty upsetting, tbh, that we all were like, "Well, that stunk, but at least we know we're immune now", only to discover that no indeed we were not.