I curate a massive list of USA-based ArcGIS server addresses. Earlier today I posted an update that includes a section listing the public-facing FeatureServer layers I know about that meet the following two criteria.
1. COVID-19 related
2. Cover the USA
If you know of any MapServer or FeatureServer or WMS layers that meet *both* of the above criteria, please let me know and I will add them to the list. I will include a note identifying the source of the data or the party doing the data collection.
The COVID-19 layer list starts at page 7 of this PDF file:
I included a link to the GISsurfer map (Lealet + GIS) I produce that can display these layers.