>>11440844That's how antibodies ideally work, but ideal is rare in medicine. Take herpes for example. Previous infection with HSV1 or 2 does not make you immune to the other. I can cause infection by the other to be more mild, but infection occurs nevertheless.
Lets say you get infected with a strain of Corona and the antibodies you produce are against the viral caspid proteins (I have no idea if this is the case or not). A new strain, read new mutation, may have an altered AA sequence in that caspid protein, making those antibodies you formed to the first strain unable to bind to the new strain. Thus, you will still be infected, and have to start from square one with your IgM response.
