So-called "immunity cards" seem so problematic. Above all, we currently don't know really anything about what type of immunity natural infection confers nor do we know how we would ascertain someone's "immune status" with a high degree of certainty. It is going to take significant research to establish these facts alone. Then, beyond that, there are significant ethical and legal concerns. I think we will make significant advances in other areas (e.g.--testing/tracing/quarantine, vaccines, treatment) before this comes into play.