(CNN) 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.

with other scientific statements about the idea of developing immunity. 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.

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