'Immunity passports' are already here. But they come with warnings

With miles of barbed wire and electric fencing along its border and open government hostility to migrants, Hungary's borders aren't always the friendliest place for foreigners. That's during normal times. Amid the pandemic, Hungary has shut its doors to almost everyone, even its European neighbors. Unless, they've had Covid-19. It's not the place you'd expect to find such a novel exception to otherwise tough entry rules. The policy, which came into force in early September, opens the door to visitors who can provide evidence that they've recovered from Covid-19 -- proof of both a positive and negative test in the past six months. Iceland has plans for a similar policy beginning next week -- and it already gives citizens who have previously been infected permission to ignore the nationwide mask mandate. Experts call these types of policies a kind of "immunity passport." But does beating the virus actually give you immunity? The evidence so far suggests that for most people, it does. "It's certainly theoretically possible that some people even who have antibodies may not be protected," Dr. Ania Wajnberg said outside her lab at Mount Sinai Hospital's Icahn School of Medicine in New York. "But I think the majority of people that test positive for antibodies will be protected for some time." Wajnberg is leading a massive study of more than 30,000 people who had mild to moderate cases of Covid-19. Her latest research published in October found that more than 90% of people have enough antibodies to kill the virus for many months after infection, perhaps longer. So the risk that someone entering Hungary under this policy could get re-infected, or infect others, is low, she says. Though the science hasn't entirely been settled on how long immunity does last for, there have only been a handful of documented cases of reinfection. "This may be a reasonable way to begin to reopen society and allow for travel and business," she says.<br/>