Coronavirus Antigen Tests Could Increase Testing Capacity : Short Wave There's a difference between diagnostic, antibody, and antigen tests. All provide different levels of reliability and speed.

NPR health correspondent Rob Stein breaks down the differences and explains why public health officials are especially hopeful about antigen testing.

Find out how your state is doing on overall testing.

Email the show at shortwave@npr.org.
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We Need More Coronavirus Testing. Are Antigen Tests The Answer?

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We Need More Coronavirus Testing. Are Antigen Tests The Answer?

We Need More Coronavirus Testing. Are Antigen Tests The Answer?

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MADDIE SOFIA, HOST:

You're listening to SHORT WAVE from NPR.

Maddie Sofia here with NPR health correspondent Rob Stein. Rob, I miss you, buddy.

ROB STEIN, BYLINE: I miss you, Maddie. It's so nice to hear your voice.

SOFIA: You too, Rob. So OK, I think by now we have all heard that testing is key to our ability to reopen the country in a safe way. Let's remind folks of why that is.

STEIN: Right. You know, ideally, we need to catch as many new infections as possible to try to prevent new outbreaks from exploding around the country. And more testing could also help reopen the economy safely by, you know, say, testing people before they go back to work or even when they get on a plane.

SOFIA: Yeah. So there are a few different tests that scientists use for some of those scenarios that we just talked about. We are going to cover each of them in a bit. But bottom line, Rob, is that we need more testing of all kinds.

STEIN: Yeah. Testing capacity is going up, which is good, but it's still nowhere near where we need it to be. For example, you know, the basic diagnostic tests - the one that tells you if you have the virus right now - we need a lot more of that.

SOFIA: That's the long swab up the nose, tickle the brain one?

STEIN: Yeah. Experts say you want no more than 10% of those tests to come back positive. That's because if you have a high percentage of tests that are positive, it's clear there's not enough testing going on to capture enough of the infected people in the community. So, you know, you want to be around 10%, and right now that number is in the U.S. is more like, you know, maybe 16%, 18% maybe even as high as 20%. So yeah, we need a lot more testing.

SOFIA: Right. Which is where a new diagnostic test comes in, a test you're here to talk about today. It's called an antigen test. The FDA just approved the first one on Friday.

STEIN: Right. An antigen test is different from the other tests because instead of looking for genetic material from the virus, it looks for pieces of the virus, proteins called antigens.

SOFIA: Right. Antigen tests have actually been used for a long time, like, to test people for the flu, for strep throat. It's actually how a lot of pregnancy tests work, too.

STEIN: That's right. They're cheap. They're fast. And public health officials say they could be the key to getting our testing capacity to the next level. Here's Deborah Birx from the White House coronavirus task force.

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DEBORAH BIRX: We have to have a breakthrough innovation in testing. We have to be able to detect antigen rather than constantly try to detect the actual live virus or the viral particles itself and to really move into antigen testing. And I know corporations and...

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SOFIA: So today on the show - how antigen testing works and why we need it in the first place. I'm Maddie SOFIA, and this is SHORT WAVE, the daily science podcast from NPR.

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SOFIA: All right, Rob. Let's talk about the other tests out there before we get to this little antigen bad boy. Sound good?

STEIN: Sounds good, Maddie.

SOFIA: OK. So the first test we've heard probably the most about, the test that tells you if you have the coronavirus right now, it's called a diagnostic test. Most of them are what's known as a PCR test. And as you know, Rob, a long time ago in a galaxy far, far away, I worked in a microbial genetics lab...

STEIN: Oh, yeah.

SOFIA: ...Where I was known, you know, to manipulate the fabric of life - DNA, RNA you name it.

STEIN: (Laughter).

SOFIA: So I can tell you that these PCR tests work by looking for a specific sequence of genetic code that belongs to the coronavirus. That allows you to, you know, specifically detect that virus that might be hanging out in your nose or throat goo. That's a scientific term, Rob - goo.

STEIN: Well, yeah. Right.

SOFIA: (Laughter).

STEIN: And generally speaking, those are the most reliable tests. But sometimes it does take a few days for the virus to show up in your nose or throat. So the tests won't necessarily identify someone immediately after they've been infected. But for the most part, it is pretty reliable. The samples are usually analyzed within, you know, hours.

SOFIA: Right. But those can take longer if testing centers have a backlog of, you know, samples or if the stuff you need to run the tests are out of stock. We saw that a lot early on in the pandemic here in the States.

STEIN: Yeah. Yeah. And it can still take days to get results in some places, maybe even longer, which has been one of the many frustrations about testing in this country. There are a couple of fast genetic tests that spit out results within minutes, as quickly as, you know, 15 minutes or so. But there are some questions about the accuracy of the quickest one of those, the one that's gotten the most attention.

SOFIA: You're talking about that little white box test from the company called Abbott Labs?

STEIN: Yeah, that's the one.

SOFIA: Right. Right. OK, so those are the genetic tests - more of those happening each week and hopefully that number will continue to go up. Let's talk about the second kind of test - antibody tests.

STEIN: The antibody tests. That's a blood test. So no swab involved, and it looks for antibodies to the coronavirus. Your body produces antibodies in response to all kinds of viral infections. They can show up in your blood in about a week or so after infection.

SOFIA: And the reason why this is important is the idea is that people who have already been infected may have some level of immunity or protection from reinfection. But we're still kind of figuring out how long that immunity might last and how strong it is.

STEIN: That's absolutely right. You know, and antibody tests, right now It's unclear how reliable they are for someone to get a test and feel confident that they have or have not had the virus. The tests that are out there, they can give, you know, false positives. They might, for example, pick up antibodies to related viruses by mistake, other coronaviruses, like maybe the viruses that cause the common cold.

SOFIA: Sure.

STEIN: But they can be useful, really useful, from a public health perspective. You get a look at how much the virus has spread and how much is out there in the community.

SOFIA: Yeah. And I will add that there's a more sophisticated antibody test out there called an ELISA, an enzyme-linked immunosorbent assay. That test is more accurate, but it is not as widely available. Fun fact, Rob - it is also the name some clowns in my immunology department gave my puppy when I was doing my Ph.D. And it stuck. Her name is Elisa.

STEIN: Aww, that is so cute.

SOFIA: (Laughter) I knew you'd like that, Rob. I knew you would.

STEIN: (Laughter).

SOFIA: OK, but here's the question. Are antibody tests going to improve to the point where we could get one that is quick and reliable?

STEIN: That's the hope, you know. In fact, the FDA is trying right now to get a better fix on how reliable the antibody tests are right now to separate the good ones from the bad ones because there's been a lot of unscrupulous companies out there making all sorts of unsubstantiated and really dangerous claims about antibody tests. So it's a really important question to answer.

SOFIA: OK, so that brings us back to this new test, the antigen test. The FDA just approved the first one on Friday.

STEIN: Right. The FDA approved an antigen test developed by a company called Quidel.

SOFIA: And these tests look for coronavirus proteins, not genetic material, kind of like those rapid strep or flu tests you might have gotten before. This type of test is really fast, but there are other advantages, too.

STEIN: Yeah. So they're actually a lot cheaper and a lot less complicated than the fancy genetic tests. So it would be a lot easier to make and use millions of them to screen millions of people every day, you know, to do things we talked about earlier like, say, a company wants to test workers every day to see who's infected and so needs to stay home and who might be in the clear can come to work that day - that kind of thing.

SOFIA: Right. But the big downside with these tests is reliability. Rob, hit me with some stats.

STEIN: So the antigen tests that have been used in the past to do things like test for strep throat or the flu, they do tend to miss a lot more infected people than the genetic tests, maybe as many as 15 or 20 out of every 100 infected people.

SOFIA: I mean, that's a lot of people, especially when you have such a huge population being tested.

STEIN: Yeah. That's the big concern and worry about antigen tests. Here's Jesse Papenburg from McGill University.

JESSE PAPENBURG: If you're using this test to screen people to make sure that they're not infected and then they can, you know, go back to work and things like that, then, you know, you're giving people the message that they're not infected when actually they are and, therefore, transmitting.

STEIN: So, Maddie, you know, other companies developing these tests are doing studies to try to prove their tests would be more reliable than antigen tests have typically been, though they acknowledge that it could turn out that their tests would have to be used to screen people and then get results confirmed by other tests.

SOFIA: Right.

STEIN: That's what the FDA is saying about the first antigen test that was just approved.

SOFIA: Rob, you said companies developing. What other antigen tests are in the pipeline?

STEIN: Well, there's a few out there that I know about. One is from a Massachusetts company that's associated with MIT, and it's developing a test that might be used on saliva, nasal swabs and blood, possibly. There's also one in Pennsylvania that's trying to develop an at-home antigen test to use on saliva. And I've also been in contact with another company out of the U.K., a company that says the tests would cost just a dollar, which would be very helpful in less affluent parts of the world.

SOFIA: OK, Rob, before we go, this is a question I think a lot of people have when they hear about testing, and that is why is testing such a mess in the United States?

STEIN: Yeah. Yeah. Well, you know, a big part of the problem is that everyone at the beginning was waiting for the CDC to make a test. And it did, but it was flawed, and it took a while for the CDC to fix that. That basically wasted really important time at the very beginning of the epidemic in this country, and we've basically been playing catch-up ever since.

SOFIA: Gotcha.

STEIN: You know, mobilizing private testing companies to get into the game, figuring out where all the labs are that can do this kind of testing. And that's no easy thing.

SOFIA: Why is that? Why is that no easy thing?

STEIN: Well, these genetic tests - you know, like the PCR test - are complicated. They require specialized machines and trained technicians, special chemicals to do them. And all of that has been in short supply because of the sudden surge in demand for testing triggered by the global pandemic.

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SOFIA: OK, Rob. I appreciate you.

STEIN: Thanks, Maddie. Always fun to be here.

SOFIA: By the way, Rob's got a big story he just did about testing rates in every state. There's a link to that in the episode notes so you can see how your state is doing.

This episode was produced by Brent Baughman and fact-checked by Emily Vaughn. Viet Le did the editing. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.

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