Health Secretary Matt Hancock announced in March that 3.5m antibody tests have been purchased to help determine who acquired immunity to the coronavirus – a crucial step in getting people back to work – but then clarified that the prescriptions were subject to testing. pending approval.
Rigorous checks on a number of test samples have so far revealed that none meet the standards agreed with the Medicines and Health Products Regulatory Agency (MHRA), forcing the government to back down allegations that the tests are ready to be sent to the public. this month.
But Martin Hibberd, professor of emerging infectious diseases at the London School of Hygiene and Tropical Medicine, said that finger prick antibody tests were rarely reliable and urged the government to focus on laboratory tests instead.
“We need a centralized pathology laboratory antibody test. The government bought these tests at home, but they are traditionally very poor in terms of sensitivity and specificity. Expecting these to work exceptionally well is unlikely in my opinion, as they do not work particularly well for any virus, “said Hibberd.
“What will the home tests be used for? What are you going to do when someone at home decides they can see a band on a strip and they go out and say I’m free, can I do what I like? I think they should give it up, “he added.
The Ministry of Health and Welfare said it had purchased its current stock of antibody tests on the basis of “minimum initial volumes”, but declined to comment on specific trading arrangements. She said that if the tests did not work, orders would be canceled and costs recovered “as far as possible”.
Sir John Bell, Regius professor of medicine at the University of Oxford, who leads the testing effort, said that the assessments were underway and that his group was talking to companies in the hopes of improving testing. antibody, adding that “a lot of very similar tests and probably come from the same factory in China”.
The Oxford group has characterized six different antibody tests and found that most are well below the required accuracy. Most did not detect the antibodies half the time, and the best detected the immune cells only 70% of the time. If used widely, the tests could leave millions of immune people convinced that they are still vulnerable to infection. For the test to pass, the accuracy should be closer to 95%.
The tests also proved unreliable to identify those who were not immune, with some declaring a blood sample positive for protective antibodies 2% of the time. This false positive is a big risk because it could mean that nurses or caregivers return to work believing that they are immunized when they are not.
Failure of the tests and the complexity of the work to improve them means that a functional antibody test could take months. The tests may not work well because they have been validated against the blood of critically ill patients and have produced a strong immune response to the virus, unlike most people, who are only slightly ill.
The global rush for antibody testing has meant that many governments have found themselves in the position of having to weigh the risks of buying poor-quality tests and having no tests at all. “The Department of Health and Welfare wanted tests quickly and felt it should be involved,” said Bell. “To their credit, they put them through rigorous tests.”
“It’s always possible that we don’t get a test … We don’t want to do a test that is bad. We want a good test that gives us the answers we want, ”added Bell.
Without a home test kit, blood samples can still be checked for antibodies using a laboratory process called Elisa, which Hibberd wants to see adopted. The Elisa test in Oxford can distinguish positive and negative blood samples with an accuracy of almost 100%. The downside is that blood has to be taken from people and sent to the laboratory for testing.
“This is the kind of test we need, not these home kits,” said Hibberd. “Will they get their money back on these tests? Who knows. Someone else will buy them, I’m sure. “