The World Health Organization is warning that people who have had Covid-19 are not necessarily immune by the presence of antibodies from getting the virus again.

“There is no evidence yet that people who have had Covid-19 will not get a second infection,” WHO said in a scientific brief published Friday.

It cautions against governments that are considering issuing so-called “immunity passports” to people who have had Covid-19, assuming they are safe to resume normal life.

“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,’ ” WHO said.

Dr. Maria Van Kerkhove from WHO has previously said it’s not known whether people who have been exposed to the virus become completely immune. The new WHO brief underscores that stance, and jibeswith other scientific statements about the idea of developing immunity.

During a Friday briefing, the Infectious Diseases Society of America warned that not enough is known about antibody testing to assume immunity.

Dr. Mary Hayden, spokesperson for IDSA and chief of the Division of Infectious Diseases at Rush University Medical Center, said, “We do not know whether or not patients who have these antibodies are still at risk of reinfection with Covid-19. At this point, I think we have to assume that they could be at risk of reinfection.”

“We don’t know even if the antibodies are protective, what degree of protection they provide, so it could be complete, it could be partial, or how long the antibodies last,” Hayden added, “We know that antibody responses wane over time.”

The society is “recommending that people with antibodies not change their behavior in any way, continue social distancing etc. And we think that this is a really important point to emphasize because we’re concerned that if this could be present, that these antibodies could be misinterpreted, people could put themselves at unnecessary risk,” Hayden said.