Back in June when the therapy was first given limited authorization, people were advised to isolate but vaccination status was not addressed, nor was the need to be tested. (https://www.reuters.com/business/healthcare-pharmaceuticals/us-authorizes-lower-dose-regenerons-covid-19-antibody-therapy-2021-06-04/)

There didn't seem to be a direct answer on the Regeneron Patient info site https://www.regencov.com/patient, but there is a phone number you can call for further help: 1-877-332-6585

Each state department of health has its own guidelines for isolation and testing by people exposed to Covid, depending on the closeness of contact and vaccination status. So if you can't get good guidance from the sources above, or your physician, I would suggest that you check your state guidelines.

I hope this helps you find the answers you need.
Sue