The World Health Organization warned on Saturday that recovering from coronavirus might not protect people from reinfection as the death toll from the pandemic approached 200,000 around the globe.
Governments are struggling to limit the economic devastation unleashed by the virus, which has left half of humanity under some form of lockdown and reported infections approaching three million.
The United Nations has joined world leaders to speed up development of a vaccine, but effective treatments for COVID-19, the disease caused by coronavirus, are still far off.
But with signs the disease is peaking in the US and Europe, governments are starting to ease restrictions, weighing the need for economic recovery against cautions that lifting them too soon risks a second wave of infections.
The WHO warned on Saturday that there was still no evidence that people who test positive for the new coronavirus and recover are immunised and protected against reinfection.
The warning came as some governments study measures such as "immunity passports" or documents for those who have recovered as one way to get people back to work after weeks of economic shutdown.
"There is currently no evidence that people who have recovered from #COVID19 and have antibodies are protected from a second infection," WHO said in a statement.
"People who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice," it said.
With more than four billion people still on lockdown or stay-at-home orders, governments are debating how to steadily lift curbs, reopen schools, restart businesses and reboot economies without causing a spike in virus cases.
Some of that discussion centres on new mobile phone apps to alert people to infections, mass antibody testing -- to determine who has had the virus and may be immune -- and the public use of facemasks to stop transmission.
"If I've already had corona then I'm not infectious," said Berlin resident Lothar Kopp, hoping to test positive for antibodies as it could allow him to visit his elderly mother.
Germany has carried out tens of thousands of tests and other countries are also working on determining what may be their so-called level of immunity.
But on Friday, UN Secretary-General Antonio Guterres called for international organisations, world leaders and the private sector to join an unprecedented effort to speed up development and distribution of a vaccine.
"We face a global public enemy like no other," the UN chief told a virtual briefing.
"A world free of COVID-19 requires the most massive public health effort in history."
The mayor of the state's capital Atlanta condemned the "irresponsible" move, telling ABC News: "There is nothing essential about going to a bowling alley or giving a manicure in the middle of a pandemic."
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