Immunity is a complicated word. It feels dichotomous in nature -- you're either immune or you're not -- but this betrays the underlying complexity of the molecular interactions of the immune system. Different variants my trigger, with some probability, recognition of some epitope which may or may not be conserved as the virus evolves.

The entire course of the infection and clearance plays out dynamically based on a multitude of factors ranging from initial viral load to immune activity and health. Depending on which cell populations are involved in the response, the response kinetics, and the degree of activation, they may proliferate this recognition for a long time or not.

It's messy.