The World Health Organisation says governments should not issue so-called "immunity passports" or "risk-free certificates" as a way of easing lockdowns.
It said there was "no evidence" that people who had developed antibodies after recovering from the virus were protected against a second infection.
The WHO warned such a move could actually increase virus transmission.
It said people who assumed they were immune might stop taking precautions.
Some governments have considered permitting people who have recovered to travel or return to work.
Restrictions imposed on movement to stop the virus spreading have crippled economies around the world.
More than 2.8m cases of the virus have been confirmed worldwide and nearly 200,000 people have died.
[Source:BBC]
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