I suppose the analogue of Jenner's cowpox innoculations would be infecting people with coronaviruses other than SARS-CoV-2 and hoping that the cross-immunity is

I suppose the analogue of Jenner's cowpox innoculations would be infecting people with coronaviruses other than SARS-CoV-2 and hoping that the cross-immunity is helpful. There is evidence for such cross-immunity, but not strong enough for this to be a strategy you'd bet on.