Coronavirus Antibody Tests Have High Rates Of False Positive

Infectious disease experts are raising pointed questions about the reliability of the early tests and they warn state and local governments — as well as individuals — should be wary of shaping policy or changing behavior based on any single report.

Antibody tests are considered to be as a crucial step to reopening the economy for good and end social distancing while we wait for a coronavirus vaccine. Antibody tests have garnered attention lately because they’re designed to show if you’ve ever had COVID-19, even if you never had any symptoms or knew you were infected. If it turns out you were, you might now be immune to the coronavirus and can possibly be around others without spreading the virus.

However, a recently released report suggests that some antibody tests had high rates of false positives.

This was revealed in screenings performed by a consortium of California laboratories.

A false positive means someone would be told they’d already had coronavirus when they had not — a potential danger as people could then think they were immune to the virus when they’re actually still vulnerable.

Of the 12 antibody tests that were studied by the COVID-19 Testing Project, one of the tests gave false positives more than 15% of the time, or in about one out of seven samples. Three other tests gave false positives more than 10% of the time.

“That’s terrible. That’s really terrible,” said Dr. Caryn Bern, one of the authors of the study that looked at the 12 tests.

She said while it’s unrealistic to think all tests will be 100% accurate all the time, their false positive rates should be 5% or lower, or ideally 2% or lower.

“This was a real wake up call for me. We’re not at the point where any of these tests can be used reliably,” added study coauthor Dr. Alexander Marson. “There’s a big danger in relying on them at all, but we hope we get to a point soon where we can rely on these tests.”

The COVID-19 Testing Project is a consortium of researchers and physicians at the University of California San Francisco, the University of California Berkeley, the Chan Zuckerberg Biohub, and the Innovative Genomics Institute.

There are high hopes for these antibody tests, which detect proteins that form in blood as part of the body’s immune response to an invading virus.

Antibody testing looks for proteins in the blood, called antibodies, which are left over after your body fights off a disease. When your immune system detects a new infection, your body starts producing antibodies, which it then trains to fight that specific invader. These antibodies figure out the invader’s weaknesses, then neutralize, destroy and ultimately remove it from your body.

After it’s gone, your body continues producing antibodies in case it ever comes back. That’s what the coronavirus antibody tests look for — the leftover antibodies your immune system produced to fight the coronavirus.

Infectious disease experts are raising pointed questions about the reliability of the early tests and they warn state and local governments — as well as individuals — should be wary of shaping policy or changing behavior based on any single report.

In the sharpest caution to date, officials with the World Health Organization on Saturday warned against plans for proposed “immunity passports,” which would allow people who have recovered from the coronavirus to resume unrestricted travel and work.

“There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” the agency wrote in a scientific brief.

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