So-called "immunity passports" were once touted as the way out of the Covid-19 pandemic, in which once someone had been infected and recovered or vaccinated they were magically free of societal restrictions imposed upon the rest of society and could now freely travel and socialize without risk. Yet even when they received considerable attention in April 2020 they were questioned by health authorities who noted that it was unclear whether a recovered or vaccinated person could still spread the disease. As the pace of vaccinations has picked up, such passports have regained interest as a way for nations to reopen travel corridors.