THAT is not proven at all. In fact, for this class of viruses, it would be exceedingly unusual.
Why?
In very brief & simplified terms:
1) The rapid and extensive mutations.
2) Covid rarely kills directly by itself. As with Flu, it's the complications that can get you. Case in point: My brother almost died of necrotic pneumonia brought on by flu. Is he now immune to flu for many years? Are you kidding?