Hopes that coronavirus antibody tests could help the UK end its lockdown have been dealt a blow – after the World Health Organization questioned whether they offer any guarantee of immunity.
The UK has placed antibody tests – which check if someone has had Covid-19 – at the centre of an eventual “back-to-work” plan to restart normal life.
But experts said they may not prove if someone is protected from reinfection.
The UK’s testing co-ordinator has also warned people not to buy private tests.
The government has already paid for three-and-a-half million antibody tests, but has not yet found one that is reliable enough to use – and stresses that it will not approve the use of any test until it can be sure its findings can be fully depended on.
Professor John Newton said the public should not purchase unapproved antibody tests until a working test is approved.
“We are breaking new ground with this work every day and I am confident this major research effort will make a breakthrough,” he said of efforts to develop a valid serology test, which measures levels of antibodies in blood plasma.
“Until then, please don’t buy or take any unproven tests. They may not be reliable for your intended use; they may give a false reading and put you, your family or others at risk.”
He added: “As soon as we have found a test that works for this purpose, we will be in a position to roll them out across the country as a back-to-work test.”
Speaking in Geneva, the World Health Organization’s (WHO) Dr Maria van Kerkhove cast doubt on the benefit of rapid serology tests due to a lack of evidence around coronavirus immunity.
She said: “There are a lot of countries that are suggesting using rapid diagnostic serological tests to be able to capture what they think will be a measure of immunity.
“Right now, we have no evidence that the use of a serological test can show that an individual has immunity or is protected from reinfection.”
She added: “These antibody tests will be able to measure that level of seroprevalence – that level of antibodies but that does not mean that somebody with antibodies means that they are immune.”
Dr van Kerkhove said it was “a good thing” that so many tests are being developed, but she added: “We need to ensure that they are validated so that we know what they say they attempt to measure they are actually measuring.”
Her colleague Dr Michael Ryan said antibody testing also raised ethical questions.
“You might have someone who believes they are seropositive [have been infected] and protected in a situation where they may be exposed and in fact they are susceptible to the disease,” he said.
The UK announced 847 new coronavirus-related deaths in hospitals in its latest figures on Friday, taking the total to 14,576.
On Friday, Health Secretary Matt Hancock said swab tests – which assess whether someone currently has the coronavirus – will soon be rolled out to other key workers, including police officers, prison staff and firefighters.
He added some 50,000 NHS workers had been tested for the virus so far.
However, he said it was “frustrating” there was currently more capacity tests each day than the numbers that were being taken up. On Thursday, 38,000 tests were available but only 21,000 were taken, hence the government’s expansion of who will be eligible to be tested.
The government has an overall target of 100,000 tests a day by the end of April.