Current COVID-19 antibody tests aren't accurate enough for mass screening, say Oxford researchers

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The U.K. government has been considering issuing “immunity passports” as part of its strategy to slowly let people out of lockdown or to allow doctors and clinicians back to work. But that would require thousands of a highly accurate, validated test. (Pixabay)

With over two dozen different molecular diagnostics now authorized by the FDA for COVID-19, the field is beginning to see the first of a new group of tests aimed at screening for people’s immune responses to the disease and cataloguing past infections instead of active ones.

While overall testing capacity of any kind remains far short of meeting demand, antibody blood tests would provide additional data on the spread of the novel coronavirus, and results showing immunity could be used to give people an all-clear to leave quarantine and return to work.

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Their accuracy would, of course, have to be paramount—any false positives could send unprotected people back into harm’s way. But researchers at the University of Oxford tasked with evaluating these serological tests say they’re still weeks away from solid validation and that no versions to date have performed well.

“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,” wrote Sir John Bell, the Regius Professor of Medicine at the University of Oxford and a government adviser on life sciences, in a university blog post.

“None of the tests we have validated would meet the criteria for a good test” described by the U.K.’s Medicines and Healthcare products Regulatory Agency, Bell added. “This is not a good result for test suppliers or for us.”

Last week, the FDA granted an emergency authorization to its first antibody blood test for COVID-19, developed by Cellex. According to the company, the test agreed with positive results from PCR tests 93% of the time and negative results 96% of the time.

In March, the agency said it considered serology tests to be less complex compared to molecular diagnostics and that it would allow their unreviewed use as long as they were not the only tests used to determine an infection. About 50 developers have told the FDA that they plan to market their tests in the U.S. without seeking an authorization. 

Meanwhile, the U.K. government has been considering issuing “immunity passports” as part of its strategy to slowly let people out of lockdown, according to The Guardian, or, for example, potentially allow quarantined doctors and clinicians to return to hospitals.

However, the U.K.’s health secretary, Matt Hancock, told the BBC that the antibody blood tests currently available for mass screening do not meet the government’s accuracy standards and would not be relied upon as the country aims to test 100,000 people daily by the end of the month.

In addition, about 35,000 National Health Service staff are currently unable to work after they or a member of their household showed symptoms, Hancock said. 

“It may be that many people get this infection without severe symptoms so many may have protection and not know it,” wrote Bell. “Large scale testing is therefore a strategy which will be crucial for getting us back to our normal lives in the coming months.”

“There are 100 or more such test kits from different suppliers available for identifying Covid-19 antibodies, and it is important that each of these is checked for accuracy before making them available to the public,” he said, adding that countries such as Spain have already returned inaccurate tests to companies.

To make sure they work, researchers need to be able analyze a person’s blood samples taken both before and after they’ve been diagnosed and recovered from the disease and examine the product alongside a gold-standard test. “It has taken some time to gather these tools for validation but the U.K. is now uniquely positioned to evaluate and find the optimal test for this disease,” said Bell. 

However, it will take “at least a month” for a test sensitive enough to be scaled up for widespread use, he said.

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