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For public health experts to begin to understand whether regular interactions between people are safe enough to resume, they will need to know if people who were infected with SARS-CoV-2, the coronavirus that causes , have developed some immunity to the virus.
Such immunity can theoretically be detected using what’s known as a serological or antibody test, which looks for proteins in your blood that your body produces after it has been infected with the virus. (This is different from the diagnostic tests that identify an active infection by looking for samples of viral genetic material, usually by sticking a swab far up the nose.)
Antibody tests may be especially important with this pandemic because it’s likely that there have been many undiagnosed cases in the U.S., according to W. David Hardy, M.D., an adjunct professor of medicine in the Division of Infectious Diseases at Johns Hopkins University School of Medicine. That’s largely because many people infected with SARS-CoV-2 don’t show clear symptoms of being ill and because diagnostic testing has not been widely and consistently available in the U.S.
Here’s what you should know about antibody tests for the novel coronavirus.
One of the reasons antibody tests may be useful is to see who has developed immunity against SARS-CoV-2. But scientists don’t actually know yet whether those who have had develop long-term immunity against the virus, according to Maria L. Alcaide, M.D., an associate professor of clinical medicine and director of the Infectious Diseases Research Unit at the University of Miami, and a fellow with the Infectious Diseases Society of America (IDSA).
After recovering from a viral infection, your immune system often develops antibodies that can protect you from getting infected again.
Sometimes that protection lasts from months to a few years, as is the case with many of the viruses that can cause the common cold. People infected with the deadlier SARS and MERS coronaviruses tend to have some protection for two to three years after infection. With some other viruses, such as measles, people infected once are generally protected against reinfection for the rest of their lives.
It’s reasonable to think that people who were infected with SARS-CoV-2 will have some protection from reinfection for a period of time ranging from several months to several years, according to Alcaide and other experts. But she cautions that it’s still too soon to say for sure.
While immunity is still “somewhat of an open question,” according to Eric Blank, chief program officer for the Association of Public Health Laboratories (APHL), initial research indicates that this virus may behave like other coronaviruses, where people have at least some short-term protection. “You might have milder symptoms than you may have experienced before,” he says. Still, we need more research to confirm people are protected from reinfection with this particular coronavirus.
How Do Antibody Tests Work?
Though there are a wide variety of antibody tests available for the coronavirus, they’re all looking for the same thing: antibodies created by your immune system in response to the coronavirus infection, Hardy says.
The first of those antibodies don’t tend to show up until five to seven days after an initial infection, Alcaide says. That’s too late to make antibody tests an ideal tool for diagnosing disease, she says. Because antibodies persist after an infection is cleared, they’re great tools for widespread monitoring, to gauge how many people in a population have been exposed to a disease.
But scientists are still learning how long antibodies last and what that means. So far, research seems to confirm that people do develop antibodies after being sick with coronavirus. Early research indicates that antibody levels decline in the first couple of months after a person clears the coronavirus infection. Levels of certain antibodies may even fall below the level they can be detected at.
If a Test Says You Have These Antibodies, What Does That Mean?
Everyone’s hope is that a positive antibody test means they can resume life in public without fear. But even if an accurate test definitively identified antibodies against SARS-CoV-2, that wouldn’t necessarily mean you are immune.
Even if tests can confirm the presence of neutralizing antibodies that will fight the coronavirus, you still might need a certain level of them in your blood to have good protection against reinfection, these experts say. We don’t yet know what that level is, and only certain types of tests can measure it.
Eventually, scientists will have a better understanding of whether most people who were exposed to SARS-CoV-2 developed enough antibodies to protect against another infection. For now though, it’s likely that we’re still months away from knowing whether people are immune after infection, Florian Krammer, Ph.D., Professor of Vaccinology at the Department of Microbiology at the Icahn School of Medicine at Mount Sinai, said on Twitter on July 13.
Can You (And Should You) Get a Test?
First, it’s important to know that antibody tests not only provide limited information, but also cannot be 100 percent accurate. The results can go wrong if the test isn’t specific enough, which means it could give you a false-positive—making it look (falsely) like you’ve been infected and have some protection against reinfection. Tests may also give a false-positive result if they identify antibodies against some other coronavirus, like the four that regularly cause common colds.
False-negative results—where a test says you do not have antibodies, but you actually do—are also a possibility. This can happen if the test is done too early, before antibodies develop, or if it just isn’t sensitive enough to detect the antibodies in your blood.
Yet even with these caveats in mind, if you spent any part of 2020 coughing and feverish, it’s understandable that you might want an antibody test.
Depending on your location, you may find your doctor’s office or a local clinic or lab offering antibody tests. (Hospitals and other medical centers that have developed their own tests are often offering them to their own staff as well as to certain patients, according to Hardy.)
You can also obtain one directly from some providers of testing services, including Quest Diagnostics and LabCorp.
Just don’t expect to necessarily get clear answers from the results, and be especially cautious of results from an older antibody test. Many of the first tests that were rolled out were fairly inaccurate, but the tests available now are better than they used to be.
The Food and Drug Administration had initially decided to relax certain regulations in order to get more testing capacity in place and so that officials could begin to see how widespread the coronavirus is in the U.S., according to Kelly Wroblewski, director of the infectious disease program at APHL. That led to an explosion of available tests, with more than 90 initially appearing on the market.
Many of those first tests were “of frankly dubious quality,” said Scott Becker, CEO of APHL, on a press call.
In May, the FDA announced new standards for antibody tests, requiring manufacturers to apply for an Emergency Use Authorization (EUA) to sell their tests, and requiring manufacturers to demonstrate that tests met a baseline standard for accuracy. An EUA should for now be considered “the gold standard” for these tests because it indicates that companies have shared testing data with the FDA, according to Becker.
Since then, the FDA has notified 68 manufacturers that their tests should be removed from the marketplace. So far, 28 antibody tests have been granted an EUA.
But there still may be poor tests available that shouldn’t be on the market. If you’re unsure about an antibody test being offered at your job or at a clinic, you can check the FDA’s website to see if it has an EUA.
Even with those tests that have an Emergency Use Authorization from the FDA, accuracy is still imperfect. Some of the first tests to receive one might still give a false-positive about 5 percent of the time—“not good enough for what we consider optimal,” Hardy says. These are first-generation antibody tests, he adds. We need more data to refine them.
For now, because of all the unknowns, take any test results with a grain of salt; don’t assume a positive result means you are immune.
Does Insurance Cover Antibody Tests?
It’s a little murky. Under the Families First Coronavirus Response Act, private insurance, Medicare, and Medicaid should cover antibody testing for as long as the tests have been authorized by the Food and Drug Administration or by your state, or have or are seeking an EUA. (The act doesn’t require that antibody tests for uninsured people be covered, however.)
Whether insurers will cover antibody tests ordered directly by a consumer, rather than by a healthcare provider, is more unclear. In general, tests directly ordered by a patient are that patient’s financial responsibility, according to Quest. HealthLabs, another company offering antibody tests directly to consumers, says it doesn’t accept insurance, but will provide receipts that consumers can submit to their insurers.
So always check with your health insurer first.
When Will We Know More?
All the tests available right now don’t necessarily answer the questions that consumers want answers to. But as the FDA and other groups review data on the tests, they’re getting a better idea of how much we know and which tests work better than others.
These reviews have helped identify some of the key antibodies these tests should be looking for, according to Blank, of APHL. “Things have changed for the better,” he says. But we still need to know how to make use of the results, since we still have more to learn about immunity.
Last, Hardy says, we will need a national strategy for who should get these tests first and how they should be administered. A coordinated national plan would ensure these tests are rolled out in a way that means people who most need to know whether they have immunity (such as healthcare workers, essential workers, and vulnerable populations) can get these tests first.
What Else Will Antibody Testing Tell Us?
Once accurate tests are in widespread use and conducted in a timely fashion, epidemiologists will be able to tell roughly how many people were actually infected with the novel coronavirus, and how many people are still vulnerable to it, says Alcaide, at the IDSA.
If, in certain communities, the prevalence of people who have already been infected is very high, that community may be protected at least temporarily, she says. But if the prevalence is still low, “that will give an indication that the population is still at a very high risk of infection, and perhaps social distancing measures should be maintained,” she says.
This could be particularly important for figuring out how extensive the initial exposure rates were for communities of color that we already know have been hit particularly hard by the pandemic, Blank says. In New York City, for example, some early data that the urgent care chain CityMD provided to the New York Times showed that in certain communities of color in hard-hit Queens, antibody levels among patients tested at CityMD topped 50 percent; at a CityMD location in a wealthier, predominantly white neighborhood in Brooklyn, only 13 percent of antibody tests came back positive.
When deciding when to relax stay-at-home and social distancing orders, health authorities are trying to avoid a second wave of infections that could overwhelm already stressed healthcare systems.
“That’s why doing these tests is so important before making decisions about reducing social distancing,” Hardy says. “It gives us an idea of what we’re dealing with.”
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