Quotes from Experts

COVID-19 testing at home

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January 19, 2022


What is known about the sensitivity of rapid antigen tests to detect the omicron and delta variants?


Gigi Gronvall, Ph.D.

“A lot of people have concerns about rapid antigen tests, that maybe they aren’t as sensitive as what has been considered the gold standard, or PCR tests. But actually they correlate really well, so at the time when you are the most infectious, when you have the most virus in your nose—and, therefore, the most virus in the air around your nose—PCR and rapid antigen tests correlate very well for omicron and delta.” (Posted January 19, 2022 | Download Video)

Gigi Gronvall, Ph.D.
Senior scholar and COVID-19 Toolkit manager, Johns Hopkins Center for Health Security; associate professor of environmental health and engineering, Johns Hopkins Bloomberg School of Public Health

Wilbur Lam M.D., Ph.D.

“So far research at many centers, including our own, has shown that the rapid tests do work against the omicron and delta variants, with a couple of caveats. One is that these rapid tests have always had not perfect sensitivity, meaning that there is a certain percentage that give you false negatives. But as long as we take that into account, the medical community and the public health community still think that these are useful tools.” (Posted January 19, 2022 | Download Video)

Wilbur Lam M.D., Ph.D.
Professor of pediatrics and biomedical engineering, Aflac Cancer and Blood Disorders Center of Children's Healthcare of Atlanta, Emory University and Georgia Institute of Technology

Nitika Pai, M.D., M.P.H., Ph.D.

“So with omicron and delta, there are not very many studies, so the data are sparse. So these tests were basically a proof of data that was obtained in many controlled environments. In real life data, there’s only one study, and that is a preprint that has been published by a group from California. And they said that they found that the sensitivity of the rapid tests in symptomatic people, right, was around as high as 97%, right, which is high. And in asymptomatics, it was as high as 89%. Now I haven’t seen the confidence intervals around it, and I haven’t peer reviewed that paper, so I will not be able to comment more on it.” (Posted January 19, 2022 | Download Video)

Nitika Pai, M.D., M.P.H., Ph.D.
Associate professor of medicine, McGill University; research scientist, McGill University Health Center

William Schaffner, M.D.

“The rapid antigen tests were developed in the era of delta—and before delta. Omicron is a little bit different. And rapid antigen tests are not quite as good at picking up small amounts of the omicron virus in your nose.” (Posted January 19, 2022 | Download Video)

William Schaffner, M.D.
Professor of preventive medicine and infectious diseases, Vanderbilt University School of Medicine

Are there steps an individual can take to avoid a false negative result from an antigen test?


Gigi Gronvall, Ph.D.

“Sometimes you may think you have COVID, or that you potentially may have COVID, but the test is saying no. And I tell people if you have symptoms, and you have contacts with people who have had COVID, maybe wait and test again in 24 to 36 hours, and your test result might be different. But act on the presumption that you might be infected and stay away from other people during that time.” (Posted January 19, 2022 | Download Video)

Gigi Gronvall, Ph.D.
Senior scholar and COVID-19 Toolkit manager, Johns Hopkins Center for Health Security; associate professor of environmental health and engineering, Johns Hopkins Bloomberg School of Public Health

Wilbur Lam M.D., Ph.D.

“Well, the bottom line is we don’t know the answers to these questions, but we’re looking into it. So scientists at other centers and our center, as well, are looking at things like the biology of the virus. Because it spreads so much [more] quickly, does it actually render the tests to be less reliable—because it’s spreading from person to person so quickly that these pieces of the virus, even when they jump from person to person, aren’t detectable by these rapid tests. We’re looking into that.

“Other things we’re looking at, the genetic mutations of the virus, could they actually adversely affect the tests themselves—looking into that. And then finally, where the virus lives—does it live in the nose, does it live in the throat, does it live in the cheek, those are all things that scientists are looking at.” (Posted January 19, 2022 | Download Video)

Wilbur Lam M.D., Ph.D.
Professor of pediatrics and biomedical engineering, Aflac Cancer and Blood Disorders Center of Children's Healthcare of Atlanta, Emory University and Georgia Institute of Technology

Nitika Pai, M.D., M.P.H., Ph.D.

“It’s important to understand that these rapid antigen tests are screening tests. And they’re very effective in a very narrow window. So the first thing that appears in your body when you get the virus is the RNA, followed by the antigen, followed by the antibody. And there is a timeline to each of these biomarkers—molecular biomarkers and immunological biomarkers—molecular RNA, immunological antigen and antibody. These rapid antigen tests are antigen based. So the best time to detect them is when you are symptomatic—and this has being underlined and emphasized by many groups—and also there is that narrow window which we say, three to seven days when peak infectiousness happens in your body. And that’s the optimal time to screen with the rapid test.” (Posted January 19, 2022 | Download Video)

Nitika Pai, M.D., M.P.H., Ph.D.
Associate professor of medicine, McGill University; research scientist, McGill University Health Center

William Schaffner, M.D.

“If you have symptoms—ah—the time to do the tests is right then. Because if you get a positive result, you can count on that positive result. If on the other hand, you’re trying to determine if you’re exposed, whether you might become positive, then it’s better to wait two or three days after your exposure before you do the test. If you do it too soon, the test will be negative, and you won’t get the answer you’re looking for.” (Posted January 19, 2022 | Download Video)

William Schaffner, M.D.
Professor of preventive medicine and infectious diseases, Vanderbilt University School of Medicine

In light of the new variants, is nasal swabbing still the best way to collect a sample for an antigen test?


Gigi Gronvall, Ph.D.

“So there’s been a lot of discussion about whether people should be swabbing their throats with omicron versus swabbing their noses. And a small study showed that some people had a positive test from a throat swab a day or two before they had a positive result from their nose swab. And then a larger study showed that the nasal swabs worked just fine. So the jury is a little bit still out on this, but you can be OK doing either. But know that the throat swabs are not authorized right now from the FDA.” (Posted January 19, 2022 | Download Video)

Gigi Gronvall, Ph.D.
Senior scholar and COVID-19 Toolkit manager, Johns Hopkins Center for Health Security; associate professor of environmental health and engineering, Johns Hopkins Bloomberg School of Public Health

Wilbur Lam M.D., Ph.D.

“As of right now we would recommend using the nasal swab because these tests have been designed and optimized and have been authorized for that specific indication. We simply just don’t have enough information to know whether swabbing other parts of the body—your throat, for example—is a good idea. But that said, a lot of scientists, including scientists at our own center, are looking into that. So we have a lot of test subjects right now where we’re swabbing all the body parts to see where the virus lives and when.” (Posted January 19, 2022 | Download Video)

Wilbur Lam M.D., Ph.D.
Professor of pediatrics and biomedical engineering, Aflac Cancer and Blood Disorders Center of Children's Healthcare of Atlanta, Emory University and Georgia Institute of Technology

What else should people know about the limits of at-home COVID-19 tests?


Gigi Gronvall, Ph.D.

“One limitation of all tests is that they are a moment in time. You can’t take a test that will tell you if you’re going to be infected tomorrow. You can’t take a test that will show if you maybe would have tested positive if you had taken the test a few hours from then. So you should always remember that when you took the sample, that’s just telling you what you need to know about that time. And so it’s not something you can carry around with you for hours and days.

“The next thing I tell people about tests is that if you’re using tests to reduce your risks of gathering with other people, test as close to the event as you can. If you’re going to meet people for dinner, don’t test at breakfast time, test a little bit closer in the afternoon or right before you get together.” (Posted January 19, 2022 | Download Video)

Gigi Gronvall, Ph.D.
Senior scholar and COVID-19 Toolkit manager, Johns Hopkins Center for Health Security; associate professor of environmental health and engineering, Johns Hopkins Bloomberg School of Public Health

Wilbur Lam M.D., Ph.D.

“No test is perfect. And I think that’s something we all have to just accept. In the case of rapid tests, false negativity seems to be its greatest Achilles heel. So we just have to keep that in mind. Now that does mean, however, that it doesn’t have a high false positivity rate. So a take-home message would be: If one of these rapid tests says you’re positive, I think you can assume you’re positive. However, if you have tons of symptoms and you’re testing negative, it may actually not be negative. So we would recommend retesting—retest the next day, maybe even test again in 48 hours, 72 hours.” (Posted January 19, 2022 | Download Video)

Wilbur Lam M.D., Ph.D.
Professor of pediatrics and biomedical engineering, Aflac Cancer and Blood Disorders Center of Children's Healthcare of Atlanta, Emory University and Georgia Institute of Technology

Nitika Pai, M.D., M.P.H., Ph.D.

“So what we need to really focus on now is to find out if we are positive with a rapid test. So that’s the most important thing, OK. And if we are symptomatic, and then we test with the rapid test, and we find ourselves to be positive, then we can be rest assured that we are positive. OK, and that’s a key message to understand. And then you have to take the next step, which is call your public health providers, call your provider and make sure that you isolate yourself, OK—and also get a confirmatory test, because essentially these tests are supposed to be screening tests. You need to get a confirmatory test afterwards. So make sure that you book an appointment to get an RT-PCR test.” (Posted January 19, 2022 | Download Video)

Nitika Pai, M.D., M.P.H., Ph.D.
Associate professor of medicine, McGill University; research scientist, McGill University Health Center

William Schaffner, M.D.

“Be sure to follow the instructions of the rapid test very meticulously. And, in particular, be sure to do vigorous swabbing in the front of your nose, both nostrils. It’s important to get a good specimen, otherwise the test won’t work.” (Posted January 19, 2022 | Download Video)

William Schaffner, M.D.
Professor of preventive medicine and infectious diseases, Vanderbilt University School of Medicine

Creative Commons LicenseThe text and video on this page are licensed as Creative Commons CC BY-SA 4.0. Journalists are free to use any text or video on this page with or without attribution to SciLine.

Gigi Gronvall, Ph.D., senior scholar and COVID-19 Toolkit manager, Johns Hopkins Center for Health Security; associate professor of environmental health and engineering, Johns Hopkins Bloomberg School of Public Health

None

Wilbur Lam M.D., Ph.D., professor of pediatrics and biomedical engineering, Aflac Cancer and Blood Disorders Center of Children’s Healthcare of Atlanta, Emory University and Georgia Institute of Technology

“Dr. Lam is a pediatric hematologist/oncologist and biomedical engineer with expertise in the development of microsystems-based point-of-care diagnostics. His laboratory receives funding from the National Institutes of Health and the National Science Foundation.”

Nitika Pai, M.D., M.P.H., Ph.D., associate professor of medicine, McGill University; research scientist, McGill University Health Center

“I have no conflicts of interest with any diagnostic company. No Board representation, etc. My implementation research program in global health is focused on rapid point of care diagnostics, for STBBI and COVID-19. I have copyrights and patents related to open access digital innovations that facilitate self testing, home testing and multiplexed testing for STBBI and COVID-19.”

William Schaffner, M.D., professor of preventive medicine and infectious diseases, Vanderbilt University School of Medicine

“I am a consultant to VBI Vaccines (they make hepatitis B vaccine) and am a past-president and current medical director of the National Foundation for Infectious Diseases (NFID), a non-profit devoted to educating both the general public as well as medical professionals about the diagnosis, treatment and prevention of infectious diseases.”