That is, if a fever is observed, what is the most likely explanation (in the US), as of today? I'm having a lot of trouble finding data on how likely it is to be COVID-19 vs something else.
The most likely cause is some kind of infection. Why on earth would you ask here instead of looking up reputable medical sources, or consulting a doctor? No one can diagnose over HN.
https://www.mayoclinic.org/diseases-conditions/fever/symptom...
Probabilities of getting any specific infection like COVID are population rates. They don’t predict individual cases.