The CDC does not grant membership to the “fully vaccinated” club until at least two weeks after the final dose in a vaccine regimen—a time that roughly corresponds to when most people are thought to acquire enough immunity to defend against a symptomatic case of COVID-19. Only then, the agency announced last week, can vaccinees start to carefully change their behavior, mingling maskless in small groups indoors, visiting the unvaccinated on a limited basis, and skipping postexposure quarantines.