Governments should not issue so-called “immunity passports” or “safe certificates” to alleviate blockages, said the World Health Organization (WHO).
He said there was “no evidence” that people who developed antibodies after recovering from the virus were protected from a second infection.
Such a move could actually increase the transmission of the virus, she warned.
People who thought they were immune could stop taking precautions, the report said.
Some governments have considered allowing those who have recovered to travel or return to work.
- Does Sweden really have its coronavirus science?
- Double warning on viral antibody tests
Restrictions on movement to prevent the spread of the virus have crippled economies around the world.
Over 2.8 million cases of the virus have been confirmed worldwide and nearly 200,000 people have died.
What did WHO say?
“There is currently no evidence that people who have recovered from Covid-19 and who have antibodies are protected against a second infection,” WHO said in a briefing note.
Most studies so far have shown that people who have recovered from an infection have antibodies in their blood – but some of these people have very low levels of antibodies.
This suggests that another part of the body’s immune response – T cells, which kill infected cells – may also be “critical” for recovery.
No study on Friday had assessed whether the presence of antibodies to the virus confers immunity to subsequent infection with the virus in humans, the WHO said.
“At this stage of the pandemic, there is not enough evidence of the effectiveness of antibody-mediated immunity to guarantee the accuracy of a” immunity passport “or” certificate safe “,” he said.
The organization also said that laboratory tests for antibodies should be further validated to determine their accuracy and should also distinguish between previous infection with the SARS-CoV-2 virus – which had caused the pandemic – and the six other known coronaviruses in circulation.
Passports too risky – for now
Analysis of Rachel Schraer, BBC health reporter
WHO advice is based on evidence from researchers around the world. But that may well change as we learn more about this virus.
There is currently no evidence to suggest that the virus has protected you once so you can no longer contract it. The idea of an “immunity passport”, allowing people who test positive for antibodies to have fewer restrictions, would therefore be very risky.
Many countries, including Germany, Italy and the United Kingdom, are starting to test samples of their populations for antibodies. In the UK, 25,000 people will be tested every month for the next year – both for antibodies and to find out if they currently have the virus.
This could provide more information on whether (and for how long) the disease provides immunity to those who have recovered. And that would give us a clearer idea of the possibility of testing individuals and granting them some sort of immunity in the future.
Where are “immunity passports” envisaged?
Last week, Chile announced that it would begin issuing “health passports” to those believed to be recovering from the disease.
Once screened for antibodies to immunize them against the virus, they could re-enter the workforce, officials said.
In Sweden, which has chosen to keep a large part of society open, some scientists believe that people can end up with much higher levels of immunity than those who live under tighter regulations.
However, Anders Wallensten of the Swedish Public Health Agency told the BBC that not enough is known about immunity yet.
“We will know more as more and more people are tested for antibodies, but also the more time passes and if more cases of reinfection, etc. are reported, “he said.
In Belgium, which has one of the highest per capita mortality rates but plans to gradually ease the lock-in restrictions from May 11, a government adviser told the BBC that he was firmly opposed to the idea of immunity passports.
“I hate the fact that we would give people passports, green or red, depending on their HIV status,” said professor of virology Marc Van Ranst, member of the risk assessment group and the Belgian government’s scientific committee on coronavirus.
“It will lead to fakes, it will lead people to deliberately get infected with the virus. It’s just not a good idea. That’s a very bad idea. “
Earlier this week, Professor Mala Maini of University College London said that reliable antibody tests are urgently needed to determine how long the antibodies persist and if they confer protection.
“We do not yet know whether these antibodies indicate protective immunity against SARS-CoV-2, but preliminary data suggests that they may be a reasonable proxy for this – so they are intended to inform release of the lock, etc. “She said.