The World Health Organization warned Saturday that there is “no evidence” that people who have had COVID-19 and test positive for antibodies are protected from reinfection. In a scientific brief seen by Reuters, the WHO warned governments against issuing “immunity passports” or “risk-free certificates” as part of a reopening strategy, adding that the practice could actually increase the risks of a second wave of the pandemic. “There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” the brief said. A number of studies have found that those who recovered from the disease do have antibodies, but the WHO insists that some have very low levels of neutralizing antibodies in their blood but not enough to guarantee cellular immunity from a reinfection.