There is no evidence people who have recovered after testing positive for the coronanvirus and have antibodies in their system won't be infected again, the World Health Organisation has warned.
In a briefing note, the WHO questioned if so-called "immunity passports" or a "risk-free certificate" would be reliable given current testing capabilities.
It's hoped these certificates could expedite people's return to the workplace.
Typically the body takes one to two weeks to develop immunity to a pathogen via an infection, the WHO said.
Studies of people who have recovered from the coronavirus typically show they have antibodies to the virus. However, some of these people have very low levels of neutralising antibodies in their blood, the WHO warned.
No study has so far confirmed that the presence of these antibodies offers immunity to a subsequent infection.
The WHO also said more work needs to be done to determine the accuracy and reliability of tests to detect antibodies to the coronavirus.
"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 WHO said.
"People who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice. The use of such certificates may therefore increase the risks of continued transmission."
