TESTING THE LIMITS — Covid seems to be everywhere in Washington, D.C., this week, from the White House to Capitol Hill to newsrooms. Even people in my home have tested positive. There’s no doubt I’ve been exposed, and I have congestion in my nose and throat. But the five rapid antigen tests I’ve taken over the course of the week, including today, have all been negative. I drove to CVS Thursday to take a PCR test. At-home antigen tests are antibody-based tests that detect proteins on the virus’ surface. These work best when people have high viral loads and are showing symptoms. PCR tests are more accurate because they test for the virus’ genetic material. While I wait for my results, I have begun to wonder whether Covid testing has become less reliable because of new variants, like BA.2. So I called Wilbur Lam, a pediatrician and biomedical engineer at Emory University. He leads a team of scientists who have been assessing Covid tests for the federal government since the pandemic began. This conversation has been edited. How well have rapid tests performed with Omicron? Rapid tests have a certain level of false negativity compared to PCR testing. Rapid tests are very useful if people have access to them and do serial testing — meaning when they get the first day of symptoms, they test and maybe they’re negative. But as they get more symptoms over the next few days, test again, and then test again. That false negativity gets mitigated somewhat. It was true for the other variants, Alpha Beta, Delta, and it’s true by and large for Omicron. Right now, our main takeaway is that, in general, tests work with Omicron as well as with the previous variants. We’re looking into, for example, maybe for people who are vaccinated, there’s a higher risk of being negative because the immune system is actually getting rid of the virus before it ends up on the swab. Do you hear a lot of anecdotes like mine, people who have been exposed but test negative? It definitely happens. But there are other viruses. The same thing happened to me just three weeks ago. I was exposed to a bunch of people. My own patients had Covid. There was this little girl I was seeing in the hospital. She was like 3 years old, and we had tested her for Covid. But the test wasn’t back yet and she was admitted for other things. I had a mask on, and when I was examining her, she grabbed my mask — she didn’t do it on purpose — and then she coughed in my face. Two hours later the lab called, “Oh, by the way, she’s Covid positive.” I kept testing myself at home, but I was always negative. Then I actually caught a cold a few days later. I never turned positive, and I got better. We’re just in this new era in society where we’re so cognizant, so vigilant. Pre-pandemic, we would be like, “I have a cold.” There’s a lot of interest among technology developers to combine at-home Covid testing with other viruses. So maybe by the start of the next flu season, we’ll have some tests that could be able to detect multiple respiratory viruses at once. What have you learned about how variants change the effectiveness of rapid tests? For a given test, there’s a shift in performance between all the different variants. Then with the same variant, there is some variability in performance among the different test brands, because they all use slightly different antibodies. The variability is nothing so significant — I don’t want to speak for the FDA, but we do report our data to the FDA — that’s making the FDA say, “We’ve got to take these off the shelves because they work so horribly.” How could we improve rapid tests? The technology behind the rapid tests has been around for decades. It’s the same type of technology that’s used for pregnancy tests. Antibodies are these biological substances that our bodies make. Antibodies, these bio-chemicals, can stick to other chemicals, and those can be mass produced. If we can improve the binding of these antibodies — make them stickier — then we could actually increase the sensitivity, meaning the tests could be able to change color at lower concentrations of virus. And PCR tests have continued to perform well with new variants? It’s actually pretty easy to determine whether a new variant will work against PCR. These tests are looking at RNA, which is kind of the brains of the virus. The way RNA and DNA is examined, it’s a line of letters. Once we can isolate the variant and do genetic sequencing, we are able to predict, “Oh, yeah, this PCR test will work.” When a variant pops up, the FDA knows exactly which PCR tests are at risk, and then they’ll tell the PCR companies to change their tests. And they’ll know exactly how to change it. With the rapid test, it’s harder to predict. As the virus evolves, it might find a way to evade the current antibodies used in the tests. Much like vaccine makers need to think ahead, diagnostic test makers need to think similarly. At some point, the tests might not work, and they’ll need either new antibodies or a new way to detect altogether. Welcome to POLITICO Nightly. Reach out with news, tips and ideas at nightly@politico.com. Or contact tonight’s author at mward@politico.com, or on Twitter at @MyahWard.
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