Scientists are warning against at-home tests kits designed to see if people who recover from COVID-19 develop immunity, saying they are often unreliable.
The UK Government ordered millions of the tests, based on the idea that if people could be shown to have previously been infected with coronavirus they could be cleared of future risk and allowed to return to work.
However, scientists have now cast doubt on the accuracy of the tests, urging officials instead to concentrate on continuing lab tests.
The home tests are meant to be able to detect antibodies which are produced by your body to fight the virus. Because the antibodies remain for months after a COVID-19 infection, their presence is a sign someone has previously had the virus, even if they showed no symptoms of it at the time.
Because experts believe that once you have COVID-19 you build up immunity to it and cannot catch it again, the antibodies would effectively give people the all-clear to cease social distancing and safely return to work.
But according to Sir John Bell, a professor of medicine at Oxford University who is in charge of testing the kits, none of them have managed to live up to expectations yet.
"There is obviously much interest in developing tests that detect these antibodies so that people know they will be safe even if exposed to those with the infection," Sir John wrote on an Oxford University blog post earlier this month.
"Sadly, the tests we have looked at to date have not performed well," he said.
"We see many false negatives (tests where no antibody is detected despite the fact we know it is there) and we also see false positives."
Sir John said that some countries, like Spain, had already sent back the test kits they had ordered that were not working, while other countries like Germany were developing their own kits but were three months away from having them ready.
Martin Hibberd, professor of emerging infectious disease at the London School of Hygiene and Tropical Medicine, told The Guardian that tests like these were rarely reliable and the government should just stick to using the traditional nasal and throat swab tests.
"The government has bought these home tests but they are traditionally very poor in terms of sensitivity and specificity," Prof Hibberd said. "Expecting those to perform exceptionally well is unlikely in my estimate because they don’t perform particularly well for any virus."
The UK Government had bought 3.5 million of the tests, according to The Guardian.
If the tests were proven not to work, the Government said it would attempt to get its money back "wherever possible"