The World Health Organisation says there is no evidence that people who have recovered from coronavirus and have antibodies are protected against a second infection.

In a scientific brief published on Saturday, the United Nations agency warned against countries issuing "immunity passports" and "risk-free certificates" that would allow people to return to work or travel, relying on "proof" that they would be protected against reinfection.

WHO reports that relying on antibodies at this stage of the pandemic could increase the risk of spreading the virus, and claims that antibody testing has not yet been proven as a reliable next step as countries look to reopen after quarantines and other mitigation efforts.

The report says: "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."

Several studies have discovered that people who did recover from Covid-19 do possess antibodies, but WHO insists that the low levels of neutralising antibodies in the blood in those cases are not enough to guarantee immunity from the disease.

The report follows Chile's announcement that it will begin issuing immunity cards functioning as passports in the country, giving them permission to clear airport security, among other permissions.

Officials across the US and in France and the UK have floated similar concepts, which presume that a person can only contract the virus once before developing antibodies to ward off another infection.

But WHO reports that "no study has evaluated whether the presence of antibodies [for Covid-19] confers immunity to subsequent infection by this virus in humans."

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WHO supports current antibody testing "at the population level or in specific groups, such as health workers, close contacts of known cases, or within households" as they are "critical for understanding the extent of — and risk factors associated with — infection."

But most of those studies "are not designed to determine whether those people are immune to secondary infections", the report says.

Several antibody tests have been launched in California and in New York, where 13.9 per cent of people in the state have tested positive for antibodies. In New York City, that figure is 21 per cent.

New York Governor Andrew Cuomo recently claimed that "large-scale antibody testing will help determine the percentage of the population that is now immune to the virus" though health officials and researchers stressed that wasn't necessarily the case, as the WHO now reports.