The person you asked is probably going to reply with a comment about the frequency of mutations being so high that no two variants are the same and so there wou

The person you asked is probably going to reply with a comment about the frequency of mutations being so high that no two variants are the same and so there would be no immunity between them, in the same way you can get the flu twice. The problem with this argument is that it applies equally to a vaccine that targets a single variant of the disease (never mind one that isn't even circulating anymore).