How are rapid COVID tests holding up as the pandemic enters its fourth year : Shots - Health News At-home rapid tests have become a staple of COVID-19 precautions, but some experts worry that people are relying too much on these tests and that's creating a false sense of security.

Is it time for a reality check on rapid COVID tests?

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ARI SHAPIRO, HOST:

It's been three years since COVID-19 was first detected in the United States. And for some, at-home COVID tests have become a part of everyday life. You dutifully swab your nostrils before a dinner party, wait 15 minutes for the all-clear, then text the host negative before leaving home. But some experts warn the tests could be giving us a false sense of security. NPR's pharmaceuticals correspondent Sydney Lupkin is here to talk about that. Hi, Sydney.

SYDNEY LUPKIN, BYLINE: Hi, Ari.

SHAPIRO: All right. There's been delta, omicron and several omicron sub-variants. Are the newer variants tripping up rapid at-home tests?

LUPKIN: For the most part, they're not. As the virus evolves, scientists are mainly seeing changes in its spike protein, which is what the virus uses to attack and enter healthy cells. But the rapid antigen tests aren't looking for that spike protein located on the surface of the virus. They're looking for a protein inside it called a nucleocapsid. And that really hasn't changed. Federal health agencies are monitoring the situation in case it does. So far, they have only identified one test that's been rendered less reliable in the face of these new variants.

SHAPIRO: Well, if the new variants are not tripping up the tests, why do we so often hear about people who test negative for days or a week and then finally learned that they're positive?

LUPKIN: You know, doctors are seeing that, but so far, it's just anecdotal. It could be driven by a few things. But Dr. Geoffrey Baird, chair of the Department of Laboratory Medicine and Pathology at the University of Washington School of Medicine, says he thinks it's probably human error. Some people even get boogers on the swab, mistakenly thinking mucus will have plenty of virus in it.

GEOFFREY BAIRD: There are some people who think that, you know, well, you rub it in my mouth and my nose and get a big glob of snot on that. It's going to - actually, you don't want snot on the thing. So some people are going to put snot on it or blood on it or something like that. You know, there's things that you're not supposed to do.

LUPKIN: There are a lot of differences between these at-home antigen tests and the PCR test done in the lab. And one of them is that the lab folks are trained, and labs are inspected to make sure everyone is doing everything right.

SHAPIRO: Can you say, relatively speaking, how well home tests work relative to the PCR tests at the lab?

LUPKIN: You know, there's certainly a time and a place for the home tests, but Baird really warns that their powers are limited.

BAIRD: Similar technology has existed for influenza for years. And the recommendation was not to use them because they didn't work because they were not sensitive enough.

LUPKIN: By sensitivity, he means they're just not as good at finding the virus as lab tests. They need more of it to register positive. But lab tests can detect the virus from trace amounts because the technology they use allows the virus's genetic material to amplify, usually over a day or two. Home tests are quicker, but they really shouldn't be used to rule out a COVID infection, according to the CDC.

SHAPIRO: And so if the recommendation is not to use at-home flu tests, should we not be relying on at-home COVID tests?

LUPKIN: You can take them and might even find out you have COVID, but take the negative with a grain of salt. It cannot guarantee that everyone is in the clear, as much as we wish that were the case. That's especially true for asymptomatic people. So in a review of more than a hundred studies looking at antigen tests, researchers found that they are considerably less accurate in people without signs or symptoms of COVID. But a positive is almost always true. Here's Dr. Robin Colgrove, a professor at Harvard Medical School and chair of the diagnostics committee of the Infectious Diseases Society of America.

ROBIN COLGROVE: The positive test is almost always true. So in a person with an exposure or a person with suggestive symptoms, if they do a test and it's positive, you're done. You have your diagnosis.

LUPKIN: And if you have COVID-19 symptoms, even if your test is negative, it's a good idea to be cautious and just stay home.

SHAPIRO: That's NPR pharmaceuticals correspondent Sydney Lupkin. Thanks.

LUPKIN: You bet.

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