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Doctors explain everything you need to know about COVID-19 antibody tests

Kells McPhillips

Kells McPhillipsMay 27, 2020

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On April 1, the Food and Drug Administration (FDA) approved the first COVID-19 antibody test: the “qSARS-CoV-2 IgG/IgM Rapid Test” created by biotechnology company Cellex Inc. The announcement came on the heels of the Mayo Clinic developing its own antibody test to be released April 6.

This development was heralded as a potential new way to see if someone has ever been exposed to SARS-CoV-2 (aka the novel coronavirus that causes the disease COVID-19), and potentially even if they are now immune to the deadly virus. Dozens of companies jumped on the antibody testing bandwagon and rushed tests to market in the past few weeks—with mixed results. But while the test may mark a promising new phase in the fight to end COVID-19 (which reached 5.4 million cases globally on May 27), there’s a lot of confusion about how the antibody test differs from existing, albeit scarce, COVID-19 testing kits. (And a lot of controversy surrounding its efficacy.)

To clear up any head-scratching, we asked Rand McClain, DO, chief medical officer of Live Cell Research, a company dedicated to enhancing health and quality of life through biological innovation, and Seema Sarin, MD, board-certified Internal Medicine physician at EHE Health, to answer all the FAQ’s about the antibody test. Including: What is it? Who will get it first? And how could it help a nation where cases are mounting by the day?

First up: What are antibodies?

“Antibodies are part of the immune system that identifies what’s called an antigen, which is a bad guy,” says Dr. McClain. Antibodies are made out of proteins, and are produced by white blood cells in direct response to the presence of these “bad guy” antigens—which can be a virus, bacteria, or even a fungus, says Dr. McClain. “The antibodies mark the bad guys so that the immune system can more easily target them and eradicate that invader.” Antibodies attach to pathogens like viruses and neutralize them, which prevents them from further replicating inside of your body.

Your immune system produces antibodies that are designed to work on specific invaders that it’s encountered before, either from prior illness or a vaccine; the antibodies that target certain forms of the flu, for example, are different from the ones that would work against something like the mumps or the measles. So someone previously infected with a virus like SARS-CoV-2 who recovered would have special, COVID-19-specific antibodies that could help fight it off if it ever came back.

What is an antibody test, in the context of COVID-19?

“The [antibody] test works by testing your blood for coronavirus antibodies to see if they have already beaten the virus and gained some immunity to it,” says Dr. Sarin. This method is called serologic testing, and it determines if someone already has the antibodies associated with SARS-coronavirus-2—which indicates that they’ve been exposed to the virus and are now potentially immune to it. The Cellex test takes blood from a person’s vein; other types of antibody tests take blood using a finger prick.

This isn’t the only case in which antibodies are used to identify if someone has immunity to a disease. Antibody tests are used to test people for antigen p24 (which is and indicator of HIV), and seasonal influenzas also use this method of testing for research purposes (not for diagnosis).

The COVID-19 antibody test produced by Cellex looks for two categories of antibodies called immunoglobulin M (IgM) and immunoglobulin G (IgG). The immune system releases IgM first when fighting a new infection, and then a version of IgG is produced later to fight the specific invader. A positive test means you have been exposed to SARS-coronavirus-2—and could be immune to it.

How does the antibody test differ from the current testing available for COVID-19?

“When you hear about testing kits for COVID-19 in the news, they’re not talking about antibody testing,” says Dr. McClain. “The test they’re talking about is designed to actually identify the virus, which they call a viral antigen or a virion, in the body. They do that with something called polymerase chain reaction (PCR) technology.” This is performed by taking swabs of a person’s nose and throat, then sending them to a lab to analyze the cultures. “And, essentially, what they’re doing is [looking for] these pieces of the virus in the body and saying, ‘oh yeah you’re infected’ or not. That’s very different than finding someone who’s already been infected and may not have known it,” he says.

These tests, says Dr. Sarin, require about 24 hours to go to a testing lab and return back to the medical facility with patient results. Antibody tests, by comparison, only take about 15 minutes to show results.

“This is simply identifying those people who have made the antibodies, and therefore it’s assumed that they’ve been exposed to the virus previously.” —Rand McClain, DO, chief medical officer of Live Cell Research

It’s worth noting that the antibody test is not a vaccine for COVID-19. “We don’t have a vaccine yet. We don’t have a treatment so far that’s been confirmed so far with ideal gold standard trials. This is simply identifying those people who have made the antibodies, and therefore it’s assumed that they’ve been exposed to the virus previously,” says Dr. McClain.

If a person has antibodies to the novel coronavirus, does that make them immune to it in the future?

Possibly, but there are some limitations. Just because you have antibodies to something doesn’t mean that those antibodies are particularly effective, virologist Angela Rasmussen, PhD, told the New York Times. Antibodies also don’t last in the body forever, which is why we have to periodically get re-vaccinated for things like whooping cough and tetanus; so a one-time exposure to the virus likely wouldn’t keep a person protected forever. Plus, the novel coronavirus is so new (it first was discovered in December 2019) that we don’t have a ton of data showing how long a recovered person would be protected from reinfection.

Thus, doctors’ expectations of immunity for this strain of coronavirus stem from their experience with other coronaviruses throughout history. “In our experience with coronaviruses—and we’ve got five of them in our history other than the SARS and the MERS that we can go back and see—is that the odds are very strong that you won’t be infected for at least another year,” says Dr. McClain. Other experts estimate that the antibodies could last in one’s system for two to three years but again, these are educated guesses.

“The problem is, some of these viruses, like the flu, mutate. Every year we have a new strain,” says Dr. McClain. Right now, the medical community just doesn’t know for sure if SARS-CoV-2 will mutate. And if it does, that could mean immunity against this year’s strain wouldn’t be quite as valuable of an asset.

“The cool thing about that, though,” says Dr. McClain, “is because the viruses have mutated, they’re still somewhat similar. So, even if it was a mutated strain, you’re likely to have better immunity than someone who’s never been inoculated with that virus.” Doctors, again, are assuming that you’ll retain some kind of immunity based on their experience with other types of coronavirus.

Why are people putting so much stock in this test for combatting COVID-19?

A number of medical professionals, Dr. McClain included, have expressed excitement about the antibody tests—first and foremost for what they could mean for the medical community. An estimated 25 percent of individuals who contract SARS-CoV-2 are asymptomatic, and a large percentage (about 80 percent) of cases are believed to be mild, so it’s likely that plenty of health-care professionals have contracted the virus, built up the antibodies, and have no idea that they’re now potentially immune.

“There are people out there who are risking their lives, literally. If we can identify that they’ve already inoculated the virus, and are therefore [potentially] immune, then [the fear of getting sick] doesn’t have to add stress to everything else is going on,” Dr. McClain says. “They can also go into work without a mask, so they don’t have to waste supplies. We can put those people on the front lines, and those who don’t have the antibodies we can choose to be more careful with.”

“If someone has developed immunity to this disease, this virus, what they’re able to do is extract these antibodies and give them to somebody else so they can better fight the disease.” —Dr. McClain

For the average citizen, the test could also be a game-changer. “People are being told to stay home, and in doing so may be losing their jobs, losing income, or may just be frustrated that they can’t get out and about to do exercise, or whatever it is,” says Dr. McClain. An antibody test that comes back positive could give the okay for someone to go back to work, or go about the normal activities that make a life.

Dr. Sarin adds that these types of tests also have the potential to give the medical community a closer look at how COVID-19 operates. “Such a test may help scientists learn how widespread the infection is, and how long people remain immune after recovering,” she says. Plus, as research fellow Larisa Labzin, PhD, of the Institute for Molecular Bioscience at The University of Queensland told The Conversation, the test could give health-care experts a better sense of what populations are more prone to infection and why—which could inform future prevention and treatment guidelines. 

Researchers and doctors are also hopeful that antibody tests could eventually pave the way for plasma therapy. “Meaning, if someone has developed immunity to this disease, this virus, what they’re able to do is extract these antibodies and give them to somebody else so they can better fight the disease,” says Dr. McClain. “That’s something that would have to be done voluntarily by those people, but we’re all humans, and I can’t imagine that there will be anything less than a fairly large percentage of the population who would want to donate their plasma.” In fact, blood centers across the United States are already beginning to gather plasma and clinical trials on plasma therapy for COVID-19 are in the works.

It’s important to caveat that antibody testing is not a silver bullet—and many issues with the tests on the market have been revealed in recent weeks. Many companies, as mentioned before, took advantage of relaxed regulations to rush shoddy tests to market, to the point where the FDA has had to step in to investigate certain tests. They also come with a big risk of false positives, meaning there’s a chance it could tell someone they have antibodies to the virus when they don’t. Even the CDC now says antibody tests may be providing false positives up to 50 percent of the time in certain populations. We also still don’t know whether the presence of antibodies equals immunity—or if it does, how long that immunity will last. So the value of the antibody test continues to be pretty theoretical.

If I wanted a test, where can I get one?

Thanks to the CARES Act (which passed in April and provides stimulus money to coronavirus testing measures, among other things), health insurance companies are required to fully cover all COVID-19 tests, including antibody tests, with no out-of-pocket expenses. Most people should be able to get one for free, although, as Money reports, your insurance plan may have particular approved providers or tests that it covers; if you visit a provider not on their list, you might have to pay a bit up front for the test.

If you’re interested in an antibody test, the best bet is to check the urgent care clinics in your zip code to see if they’re offering the tests. CityMD, for example, is offering the tests throughout its New Jersey and New York locations. You can also visit a LabCorp (a patient care-oriented drug developer) near you to get tested on-site. (The test itself is free, but they do charge a $10 fee for the physician order of the test.) Just be sure to cross-reference with your insurance company to make sure that a visit to those clinics will be covered. It also can’t hurt to run any and all of these options by your primary care doctor to hear their recommendations for moving forward with a test. Either way, take those results with a grain of salt, and be sure to still practice safe social distancing, hand washing, and mask wearing.

This post was originally published on April 3, 2020; updated on May 27, 2020.

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