New Zealand has another coronavirus-related death - a man in his 60s from the Rosewood Rest Home in Christchurch. The country also has five new Covid-19 cases today - two confirmed and three probable.
The World Health Organisation (WHO) has warned against handing out "immunity passports" to people who have recovered from the coronavirus, saying there is "no evidence" they are protected from catching the disease again.
Several countries anxious to reboot their economies have floated the idea of issuing "immunity certificates" to people who have had Covid-19, officially clearing them to leave their homes and travel to and from work.
Those who have been exposed to the disease would be identified using antibody tests, which can rapidly detect the presence of antibodies in a person's blood through a simple finger prick.
But in a scientific brief, the WHO said there was "currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection".
Rapid blood antibody tests from China check for proteins that develop a week or more after someone is infected. Photo / AP
"Studies show that people who have recovered from infection have antibodies to the virus. However, some of these people have very low levels of neutralising antibodies in their blood," it explained.
To date, no study had evaluated whether the presence of antibodies to Covid-19 in humans resulted in immunity, it said.
The global health agency also warned that handing out immunity certificates could lead to a resurgence of the virus.
"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," it said.
Many governments have rushed to buy millions of antibody tests as they plan their virus exit strategy.
UK Prime Minister Boris Johnson called the tests a "game changer" and ordered 3.5 million home tests from various Chinese companies.
A woman holds her hand out to have blood collected for a 15-minute test for Covid-19 coronavirus antibodies at a drive-thru site in New York. Photo / AP
New York Governor Andrew Cuomo also announced a massive rollout of antibody testing in his virus-ravaged state this week.
But Australia's Health Department last month said "point of care" tests that detected antibodies were yet to be rigorously tested by the Therapeutic Goods Association (TGA).
"Many countries are now testing for Sars-CoV-2 antibodies at the population level or in specific groups, such as health workers, close contacts of known cases, or within households," the WHO said.
"WHO supports these studies, as they are critical for understanding the extent of – and risk factors associated with – infection.
"These studies will provide data on the percentage of people with detectable Covid-19 antibodies, but most are not designed to determine whether those people are immune to secondary infections."
The head of the WHO's emergencies programme, Dr Mike Ryan, has previously said there is "lots of uncertainty" surrounding antibody tests.
More than 2,800,000 cases of coronavirus have now been confirmed across the world and nearly 200,000 people have died.
