There is no proof that COVID immunity is even possible at this point, the only way to test it would be to expose someone again to the virus, which is unethical.
I think that's a bad action, and maybe that way won't work because everyone's immune condition is very different so it won't be easy to get people to catch Covid when the immune condition in the body is good. maybe trump is easy to get because his body condition is weak because maybe he is too tired and doesn't use a mask so he can easily catch it