Mayo Clinic unveils key COVID-19 antibody test

A test that could help determine whether people gain immunity after a COVID-19 infection was announced Thursday by Mayo Clinic and its corporate partners.

The test is the first in the world that will be broadly commercially available to identify neutralizing antibodies — the proteins produced after COVID-19 that will fight off the coronavirus if it comes back. Existing tests developed amid the pandemic show whether people have produced any antibodies in response to the illness, but not these key proteins.

"This is more reassuring than just ... a positive [antibody test] to show you have been previously exposed to the virus," said Dr. Stephen Russell, chief executive of Vyriad, the Rochester, Minn., company that created the test and provided it to Mayo via a licensing partnership with a second company, Regeneron. "This test is showing what level of protection you actually have."

Vyriad and Mayo leaders cautioned that the test can't yet give "immunity passports," or suggest that people are no longer at risk after recovering from the illness.

Nobody knows the amount of neutralizing antibodies needed to fight off reinfection, so a test that merely finds them is insufficient to prove immunity, said Elitza Theel, director of Mayo's infectious diseases serology laboratory.

Research has shown varying antibody levels in patients who have recovered from COVID-19, including as many as 5% with no antibodies.

The test is available to Mayo clinicians and researchers now and to others in late June.

This incremental advance might frustrate those who are hungry for proof of COVID-19 immunity, but it will accelerate research to answer that question, Theel said.

"It's been kind of the story for antibody testing from Day One. There was a lot of excitement, as there should have been, but at the same time we didn't really understand the role of antibody testing, and I think there was, to some extent, overexcitement," she said. "But with the neutralizing antibody test, I would view this as another step, another tool that we can use to better understand our immune response to [the virus]."

Mayo and the University of Minnesota developed some of the first COVID-19 antibody tests, raising hopes that state health officials could identify people who have recovered and declare them safe to return to work and move about in society without fear of infection. That hasn't come to pass yet, but the prospect remains.

Studies in monkeys have suggested immunity after infection with the SARS-CoV-2 virus that causes COVID-19. Studies of the global SARS pandemic in 2003 showed two to three years of immunity for people who had been infected by the SARS-CoV-1 virus.

Establishing the spread of COVID-19 in Minnesota will be critical given predictions of a second wave of cases.

The Minnesota Department of Health on Thursday reported 453 lab-confirmed cases and 13 deaths, raising the toll of the pandemic to 29,316 cases and 1,249 deaths — including 994 deaths of residents of long-term care or assisted-living facilities.

The state reported on Wednesday 12,071 COVID-19 diagnostic tests, which identify the active presence of the virus in nasal or throat swabs. Diagnostic tests are different from antibody tests that confirm infections after recovery.

While growth in COVID-19 cases has ebbed in June, it's unclear what happens next, said Jan Malcolm, state health commissioner. "We frankly have no idea where it goes from here, whether it stays in this pattern."

The Institute for Health Metrics and Evaluation in Washington offered its first modeling predictions over a second national wave, starting with an uptick in deaths in August and September due to less compliance with social distancing. The institute predicts 2,193 COVID-19 deaths in Minnesota by Oct. 1.

Existing U and Mayo antibody tests are being used in population studies to assess how many people already had COVID-19 — which is a mystery due to the number of people who never have symptoms but carry and spread the virus.

The U amassed results of antibody tests for hospital workers and clinic patients and submitted the data Thursday to a medical journal for publication. It is also studying whether antibodies can be found in saliva rather than blood serum.

The U is developing a neutralizing antibody test but also is researching whether the total number of antibodies in patients is a proxy for the amount of neutralizing antibodies they carry, said Marc Jenkins, director for the U's Center for Immunology.

"Then that [ordinary] antibody test becomes a lot more useful than it is now," he said.

Mayo's national lab has performed more than 100,000 antibody tests, and the U has processed tests as well for clinicians whose patients needed to know their status. Risk patterns with COVID-19 have become clear, with the elderly being at greatest risk of death along with people with underlying health conditions such as diabetes, obesity and diseases of the heart, lung, kidney and immune system.

A key biological feature of the COVID-19 virus is a "spike" protein on its surface that helps it bind with receptors and invade human cells.

While other antibodies act as triggers to activate the immune system to fight infection, the neutralizing antibodies bind to the virus on their own and block its ability to infect cells.

Verifying the presence of neutralizing antibodies so far has required working with the coronavirus, which can be studied only in controlled biosafety level 3 labs by researchers in protective suits.

Vyriad created a safer look-alike virus with the SARS-CoV-2 spike, which can then be tested against people's blood serum to see if neutralizing antibodies emerge. Tests with this virus can occur in less-restrictive level 2 labs, which exist in many hospitals.

"We can do it without the bunny suits," Russell said.

For starters, Mayo will use the test for neutralizing antibodies to assess people who have recovered from COVID-19 for donating plasma.

Mayo is leading a national trial to see if this convalescent plasma treats severe COVID-19. So far, the study has tallied more than 29,000 donors and 21,000 recipients.

Plasma rich in neutralizing antibodies could be particularly effective, Russell said, but plasma lacking these proteins could have an opposite effect and stimulate the virus.

"You do not want to be giving people low concentrations of antibodies," he said. "You thereby run a risk of making things worse. So having a test for neutralizing antibodies that can discriminate between low, intermediate and high [levels] is pretty important."

The neutralizing antibody test also could help in the distribution of vaccines against COVID-19, once they are available. Theel said initial vaccine quantities could be limited, so antibody testing could assess who needs them the most.