I don't care to much about the ethics at this point, but I think they would get plenty of volunteers in prisons and jails to test the vaccine on. The ones that refuse would be control cases. I would even say they should knock a month or two off of their sentences if they volunteer. Nursing homes and active senior living places would be another good test case to pull volunteers from. Especially if they aren't going to follow the mask and isolation guidelines. Doctors who work with covid patients would be another group i they haven't been infected already.