Antibody tests for coronavirus hold promise, but they’re not yet reliable enough

Chicagoans who have a burning curiosity to know whether they’ve been infected with the coronavirus can get an antibody test at a healthcare clinic for about a hundred bucks.

The problem is that no one can say for sure what the test results mean.

Despite a proliferation of COVID-19 antibody tests that are now available, having been churned out hastily under emergency conditions, the science that will help explain whether the antibodies offer future immunity isn’t there yet.

And a recent examination by some of the nation’s top scientists found unacceptably high rates of false positives in some antibody tests, calling into question their usefulness.

As more states inch toward reopening their economies, experts caution that antibody tests are just one tool and an imperfect one at that.

“It’s very early. We need to do so much more work,” says Dr. Mary K. Hayden, chief of the division of infectious diseases at Rush University Medical College and spokeswoman for the Infectious Diseases Society of America.

Antibody tests are different from the molecular nasal swab tests used to detect the presence of live coronavirus in an infected person.

The antibody test takes a small amount of blood to look for the presence of antibodies produced by the body’s immune system in response to an infection. With COVID-19, antibodies usually appear a week or more after the onset of symptoms.

Much hope has been placed on antibody tests, on the theory that knowing whether people have been infected in the past might show whether they have enough immunity to safely return to work or school. The results also potentially could show who is qualified to donate blood for convalescent plasma, which is being used investigationally on very ill patients.

There are several concerns, though. The first is accuracy. The majority of antibody tests were manufactured without approval from the federal Food and Drug Administration, which offered “regulatory flexibility” for test developers due to the pandemic.

While swab tests used to diagnose live virus must have an “Emergency Use Authorization” from the FDA, only a handful of antibody tests have made it through that process.

U.S. Rep. Raja Krishnamoorthi, D-Illinois, who chairs a House panel investigating whether the antibody tests work as advertised, has urged the FDA to better police the test-kit manufacturers and pull faulty tests from the market.

The FDA has said the National Institutes of Health will evaluate the tests.

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The COVID-19 Testing Project — a joint effort of the University of California-San Francisco, University of California-Berkeley, the Chan Zuckerberg Biohub and the Innovative Genomics Institute — tested 14 coronavirus antibody tests and found that only one delivered no false-positive results, meaning it never detected antibodies in someone who was never infected.

Two others came close, delivering no false positives nearly 99% of the time.

The 11 other tests did not fare as well. Four had false-positive rates ranging from 11% to 16%, and many of the others were around 5%.

Even the three highly accurate tests gave false-negatives about 10% of the time, which means some people who had been exposed to the virus weren’t flagged by the tests.

Poor quality tests could have huge implications if large numbers of people were told they had survived an infection of COVID-19 when they actually had never been exposed to the virus.

Getting a false positive reading 10% of the time or more “definitely I would consider unacceptable,” says Patrick Hsu, a bioengineering professor at UC-Berkeley who is helping lead the COVID-19 Testing Project.

Hsu says he was intrigued by the tests, with at least 150 now available and consumers eager to be tested. “Yet these had not been rigorously or systematically evaluated,” he says.

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Even if an antibody test is accurate, no one knows what a positive result means beyond confirming past exposure to the virus. Whether it might give you immunity in the same way that, say, having had chicken pox against getting that disease again does hasn’t been shown.

Experts at Johns Hopkins University caution that “antibody levels have not been correlated with immunity” and that, “while people who have been infected are presumed to have some immunity, it is unclear how much and for how long.”

The World Health Organization says, “There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.”

Scientists also are trying to figure out whether people who’ve had a really bad illness with COVID-19 produce more antibodies than those who’ve had only mild symptoms or were asymptomatic.

The notion that a positive antibody test gives someone an “immunity passport” to resume normal life is dangerous, according to Hsu, who says, “There are a lot of unknowns here.”

For now, antibody tests are more useful in giving a wide-lens look at where the virus already has swept through and where it has yet to arrive, Hayden says.

A large-scale testing program could be used to compare geographic communities or population groups with each other, providing they were “apples-to-apples” comparisons, Hayden says.

More testing also could help pin down more accurate death rates.

The federal Centers for Disease Control and Prevention and the NIH have announced plans for testing.

Accuracy is important because, in communities where the coronavirus hasn’t heavily penetrated, false positives would make up a greater proportion of all the positive results and might even outnumber the true positives.

The bottom line: Antibody tests aren’t a get-out-of-jail-free card for antsy people hoping to get back to their old lives.

But it’s not all doom and gloom, Hayden says.

Besides working to understand how the coronavirus antibodies function and refining the tests, scientists are developing tests that could detect viral antigens, which would be another way to catch infectious patients at an early stage. They’re also working on a vaccine and testing drugs.

“Four months ago, we didn’t even know this virus existed,” Hayden says, noting the fast progress scientists have made. “But we have a lot to do and a lot to learn.”