What We Know About COVID-19 Antibody Testing

Many are paying out of pocket for the tests, as well as incurring unexpected lab bills after the fact. Does having antibodies for a virus mean I’m immune to the virus? We can’t say that immunity is going to last forever.”

What are “immunity passports”? Not all antibodies are the same, and they vary as to whether they actually neutralize their corresponding viruses and for how long. It does mean, though, that it could make testing for antibodies more difficult.)

Casanovas-Massana said this misinterpretation is “perhaps the biggest risk” related to antibody testing — that people will incorrectly equate the presence of antibodies with immunity. When disease-causing agents called pathogens enter your body, your immune system — which includes white blood cells, antibodies, and stem cells, among other things — mobilizes to destroy them. “Even if you were exposed, wear a mask,” she says. Health experts think that antibodies for SARS and MERS coronaviruses last about a year, and there is hope the SARS-CoV-2 virus will react similarly, but there is, as of right now, no proof that it does. “If people think their employment, or their travel, or anything else that’s financially important to them is going to rely on getting or having been exposed, it means you’re going to get fraudulent passports, and you’re going to get people deliberately trying to get infected.” This is bad for the obvious reasons — that it is good to not get sick — and also because we do not know yet what the long-term effects of the virus are. Testing is never going to be 100 percent accurate, but antibodies tests are now thought to be 95 percent to 99 percent specific. “A lot of people would be left out of that,” says Gronvall. As you may know, testing to diagnose a current SARS-CoV-2 infection involves a nose swab. They could help the more vulnerable population. (Gronvall points out that this doesn’t necessarily mean you can be reinfected; the immune system is complicated, and immunity might come from another aspect of it. If you have insurance, check with your provider before your appointment to confirm that it will cover the cost. “People could stop wearing masks or social distancing — the common things that still need to be in place,” he says. is, according to the New York Times, between 5 percent and 15 percent; this means we could be getting false positives up to half of the time. What are antibodies? Because there is so much we don’t know, Gronvall urges patience and caution. Beyond that, for antibodies to fight off a second exposure to a virus, you need a certain level of the sort of antibodies that will be effective in doing so, which are called “neutralizing antibodies.” If that antibody level dips below what is necessary to protect you, you’ll be vulnerable to the virus again. The answer is not necessarily, both in general and with the SARS-CoV-2 virus specifically. It’s a confusing situation, so we’ve attempted to untangle it here with the help of Gigi Kwik Gronvall, an immunology expert with the Johns Hopkins Bloomberg School of Public Health, and Arnau Casanovas-Massana, who specializes in the epidemiology of microbial diseases at the Yale School of Public Health. Since most people are paying for the antibody test out of pocket, and since the usefulness of the result is unclear, many people are getting tested only once, lowering the statistical confidence in their result. The thought process goes like this: If you were at some point exposed to the SARS-CoV-2 virus, you will produce antibodies for it, which will keep you immune for some reasonable chunk of time — at least long enough that there would be a vaccine by the time your immunity faded. As you know, it is currently unknown whether having been infected means you are immune, either temporarily or for any significant length of time. “That would drive the statistical confidence you have in that test,” says Gronvall. “Numerous companies appear to be marketing fraudulent tests.”

Luckily, the FDA updated its standards in May. But according to the World Health Organization, it is unclear if immunity even exists for the SARS-CoV-2 virus. And this would lead to the next issue. “We have to wait and see what happens in the next months and years. The so-called immunity passports, or immunity certificates, would be granted to those considered immune and would allow holders to return to work, travel, and to whatever else. Walsh’s explanation over at Intelligencer to be helpful. This is confusing and counterintuitive, but I found James D. The National Cancer Institute is also working to evaluate commercially available antibody tests in order to provide the FDA with independent research. Even though tests are now fairly reliable in terms of their specificity, a test’s accuracy is also determined by the rate of infection in the population. The trouble with the SARS-CoV-2 virus is that it is unknown whether antibodies, rather than another arm of the immune system, are what the body uses to fight the virus; beyond that, it is unknown what level of antibodies are needed and for how long that level might keep a person immune. They could travel. She compared it with HIV testing: “If you got a positive HIV test, they would immediately follow that up with another test.” If there was a low prevalence of disease in the surrounding population, you would have a third test on top of that. “So it’s like: How long are you going to keep this passport, and what are the conditions for it, and how are you going to reevaluate it?” she says. Unfortunately, use of the passports relies on a different reality. To get antibody tests on the market quickly, the Food and Drug Administration waived its requirement that they be reviewed and approved by the FDA. Are the antibody tests that are available for the SARS-CoV-2 virus accurate? Unfortunately, that’s how it is.”

“What a positive antibody test will tell you, if it’s an accurate test, is that you have been exposed,” Gronvall says. Sensitivity means the test is able to find the antibodies related to SARS-CoV-2 exposure; if the test isn’t sensitive enough, you might get a false negative. Antigens are protein elements found on the surface of pathogens; they alert the body to an infection and trigger an immune response. Right now, the base rate of infection in the U.S. Specificity means the test is specific enough to know the antibodies it found are the antibodies related to SARS-CoV-2 rather than something else; if the test isn’t specific enough, you could get a false positive. “Not everybody is going to have an easy time with this virus. In fact, a new study published in Nature Medicine suggests antibodies may only last for two to three months. Some tests are better than others. Even if immunity were known and qualifiable, Gronvall says the concept of a passport could pose serious risks. A lower prevalence of the infection means a higher risk of getting false positives. But test accuracy also depends on disease prevalence. “We need time to prove immunity,” he says. Being “approved” under a EUA is still not as strict of a process as the FDA would otherwise undergo, but it does require an FDA review of testing done internally by the test manufacturer. But the difference between a positive HIV-test result and a positive antibody-test result is that the former has significant meaning in terms of the need to seek treatment. How are antibody tests administered? “We don’t know exactly what amount of neutralizing antibodies is enough to control the disease or how long this protection lasts. That immune response is the production of antibodies. Something Gronvall says could help is testing multiple times. Let’s say I’m confident in my test result. You can’t hide out in your house forever, but there is no decision that could come from this antibody test that is going to be a total Get Out of Jail Free card.” But testing for a past infection, by looking for antibodies in your blood, involves a blood sample. Now, companies that manufacture tests have to submit a request to be reviewed under Emergency Use Authorization (EUA). Instead, antibody tests entered the market with only the manufacturer’s claim of accuracy. Another issue is that, although it might not seem this way, particularly in comparison with other countries, the prevalence of the disease in the U.S. Three months, a year, ten years — we don’t know,” says Casanovas-Massana. During the test, a health-care provider will draw a sample of your blood and send it to a lab for testing. Some governments, including those of the U.K., France, Chile, Italy, and the U.S., have announced that they would consider “immunity passports” as part of their plan to reopen society. By Kelly Conaboy@kellyconaboy

Photo: dpa/picture alliance via Getty Images

Many are hopeful that antibodies could be the savior of the coronavirus pandemic. The first is that we still do not know how long immunity, if it exists, lasts. Test accuracy mainly depends on two things: sensitivity and specificity. The answer is fairly complicated and somewhat maddening, so let’s break it down into hopefully easier to understand elements. is technically low. “We can’t say that antibodies, or a certain level of antibodies, means that you’re immune or not. (Gronvall says she thinks it’s around 10 percent at most.) Because of this, offering an immunity passport would only welcome a very small percentage of the population back to society. “FDA has failed to police the coronavirus serological antibody test market,” the report said. In late April, the House Oversight and Reform Committee released a report about how this led to a glut of inaccurate tests. So the existence of antibodies in a person’s blood means they have been exposed to a pathogen, which, in this case, is a virus. In this version of the future, people with antibodies, perhaps holders of so-called immunity passports, could go back to work. Still, antibody testing is available, and those who know or think they might have been infected with the virus have the ability to be screened.

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