The World Health Organization is cautioning against the idea of "immunity passports." It says there is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected against a second case of infection.

The concept of "immunity passports" or "risk-free certificates" has been floated as a way of allowing those protected against reinfection to return to work.

However, the Geneva-based U.N. health agency said in a scientific brief released Saturday that more research was needed. It says that "at this point in the pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an ‘immunity passport’ or ‘risk-free certificate.’"

The organization argues that the move may encourage those who assume they are immune to reinfection to ignore public health advice and that such certificates could raise the risks of continued virus transmission.

The WHO added that tests for antibodies of the new coronavirus also needed "further validation to determine their accuracy and reliability."