BERLIN: 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 infection.The concept of “immunity passports” or “risk-free certificates” has been floated as a way of allowing people protected against reinfection to return to work.But the Geneva-based UN health agency says in a scientific brief released Saturday that more research is 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.'”It argues that people who assume they are immune to reinfection may ignore public health advice, and such certificates could raise the risks of continued virus transmission.WHO adds that tests for antibodies of the new coronavirus also “need further validation to determine their accuracy and reliability.”