COVID-19 Antibody Tests Proliferate, but What Do They Show?

Kate Johnson

April 22, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Noopur Raje, MD, has been sitting at home for 5 weeks waiting for her COVID-19 test to turn negative so she can get back to work. She's a cancer specialist ― head of the Massachusetts General Hospital's Center for Multiple Myeloma ― but Raje says as soon as she's allowed back to the hospital, she'll head straight to the front line of COVID-19 caregivers.

"It's people like us who have to get back in the trenches and do the work now," she told Medscape Medical News.

"I still will be at risk," she said. But, having nursed her physician husband through COVID-19 at home until he was admitted to an intensive care unit, she is determined to help in the COVID-19 wards.

"I will be the first one to volunteer to take care of these patients," she said. "I can't wait, as I want to give these folks hope. They are so scared."

Around the world, it's assumed that she and others like her who've recovered from COVID-19 will be immune to the infection.

Some have suggested that with antibodies to the virus coursing through their veins, these survivors might be given immunity passports. They could be the ones to jump-start people's lives again ― the first to be let out from lockdown, and in healthcare, the ones to head the ongoing battle against this pandemic.

So, there has been a race to develop COVID-19 antibody tests to identify these people.

Circumventing the Usual Clearance Process

To speed up the process, the US Food and Drug Administration (FDA) made a much-criticized move to allow a free-for-all for developers to begin marketing antibody tests that had not gone through the agency's usual evaluation process. The result was a flood of more than 90 unapproved tests "that have, frankly, dubious quality," said Scott Becker, CEO of the Association of Public Health Laboratories (APHL), which represents local and state public laboratories.

The APHL spoke out in dismay ― its chief program officer, Eric Blank, decried the "Wild West" of tests unleashed on the public.

"These tests create more uncertainty than before," said Kelly Wroblewski, APHL's director of infectious diseases, in a news conference on April 14. "Having many inaccurate tests is worse than having no tests at all."

The APHL and the FDA, working with the Centers for Disease Control and Prevention and the National Institutes of Health (NIH), have moved quickly into damage control, conducting evaluations of the tests in an effort to distinguish the potentially useful from the useless.

So far, they have succeeded in issuing emergency use authorizations (EUAs) to only four tests, those marketed by Cellex, Ortho Clinical Diagnostics, Chembio Diagnostic Systems, and the Mount Sinai Laboratory.

For all the other antibody tests on the market that do not have an EUA, "They're trusting that the test developer has done a good job in validation," Becker said. But there are worrying anecdotes. "Our members have reported that they've seen fraudulent marketing.... We've seen the FDA clamp down on some companies... [and] a number of cities and health departments have issued warnings because of what they've seen," he added.

In particular, Wroblewski said, some companies are marketing tests for use in physicians' offices or pharmacies. "Today, there are no serology tests approved for point-of-care settings," she warned. "We don't know how to interpret the test results, if the presence of antibodies indicates immunity, how long it will last, or what titer might be sufficient."

Uncertainty Emphasized

The FDA emphasized the uncertainty about antibody tests in a statement released on April 18.

Although the tests can identify people who have been exposed and who developed an immune response to the virus, the agency noted, "we don't yet know that just because someone has developed antibodies, that they are fully protected from reinfection, or how long any immunity lasts."

The FDA says that the role of these antibody tests, at present, lies in providing information to "help us track the spread of the virus nationwide and assess the impact of our public health efforts now, while also informing our COVID-19 response as we continue to move forward."

The World Health Organization (WHO) also emphasized the current uncertainty over antibody tests at a press briefing on April 17. "Nobody is sure about the length of protection that antibodies may give and whether they fully protect against...the disease," said Mike Ryan, MD, executive director of the WHO's emergencies program. There is also a concern that such tests may give false assurance or be misused. "There is still a lot of work that needs to be done to validate these antibody tests," he added.

"The WHO are right to highlight that any antibody test, if we get one, won't be able to definitely say whether someone is immune to the infection, because we just don't know enough yet about how immunity works with COVID-19," commented Prof Chris Dye, Oxford Martin School, University of Oxford, in reaction on the UK Science Media Center.

Expanding on this point on the same site, Andrew Easton PhD, professor of virology at the University of Warwick, noted that "a serology test does not discriminate between neutralising and non-neutralising antibodies; a discriminatory test is much more complex and slow."

Only the neutralizing antibodies have the ability to inactivate the invading virus, he noted.

"When people are infected, the proportions of neutralising and non-neutralising antibodies can differ. It is not always understood what makes an antibody neutralising and another non-neutralising, or why an infection leads to production of more of one of these types of antibodies," he explained. "The initial immune response immediately following infection sets the memory of the immune system, so if the person had generated mostly non-neutralising antibodies, the next time that person encounters the same virus, they may not be able to prevent an infection."

So at present, the information from antibody testing is largely unhelpful to individuals, but it could be valuable to epidemiologists and policy makers.

"States are looking at ways they can integrate reliable serologic tests for surveillance," explained APHL's Blank.

Knowing how widespread the infection has been within a community could guide research and possibly public health decisions, Wroblewski said at the APHL press conference. But she's hesitant here, too. "I know there has been a lot of talk about using this testing to ease restrictions, but I do think we need to be cautious on how quickly we move in that direction." If people don't have antibodies, it means they haven't been exposed and that they're still vulnerable, she noted. "If nothing else, that still informs policy decisions, even if they're not the policy decisions we want."

Trials Recruiting, Medical Centers Develop Own Tests

Despite the uncertainties over antibody testing, many efforts are still being guided by this strategy.

The NIH is recruiting volunteers to its antibody testing study and suggests that immunity is "likely" for those who test positive.

In addition, several large medical centers have developed their own antibody tests, including Stanford, the Yale New Haven Hospital, and the Mayo Clinic.

The Stanford test detects two types of antibodies: IgM, which is made early in an immune response and usually wanes quickly, and IgG, which rises more slowly after infection but usually persists longer.

"There's limited data out of China and Europe showing that this appears to be the response pattern followed with this virus," commented Thomas Montine, MD, PhD, professor and chair of pathology at Stanford University. "But no one has had this long enough to know how long after infection the antibodies persist," he added.

"There is enormous demand for serologic testing," said William Morice, MD, PhD, president of Mayo Clinic Laboratories. "At this time, serology testing needs to be prioritized for efforts to identify individuals in areas where potential immunity is key ― supporting healthcare workers, screening for potential plasma donors, and helping advance the most promising vaccine candidates."

During a recent webinar with the Association for Value-Based Cancer Care, the largest physician-owned oncology-hematology practice in the country, the president, Lucio Gordan, MD, said his organization was looking into antibody testing for staff. "They wanted to see how many have been exposed," he said, although "what it means is uncertain."

When Medscape Medical News checked back with him a few weeks later, Gordan, president of Florida Cancer Specialists and Research Institute, reported that no progress had been made.

"We unfortunately have not been able to test yet, due to concerns with reliability of kits. We are waiting for a better solution so we can reassess our strategy," he said.

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