I was reading Schoeman, 2019 which describes possibilities for live attenuated vaccines for SARS. For example, the complete deletion of the envelope (E) protein is said to attenuate the virus. Several drugs have been proposed for use against SARS-CoV-2 as E-protein inhibitors. Alam, 2020 preprint This raises the question of whether you could make a simple delta E mutant of the virus, comparable to one which might arise by random mutation, and expose people to it in the manner of cowpox. Such an approach might be used as by a society with widespread infection and (apparently) very little biomedical infrastructure. But have any experiments of this type been done?