Why Do Rapid Tests Feel So Useless Right Now?


Max Hamilton found out that his roommate had been exposed to the coronavirus shortly after Thanksgiving. The dread set in, and then, so did her symptoms. Wanting to be cautious, she tested continuously, remaining masked in all common areas at home. But after three negative rapid tests in a row, she and Hamilton felt like the worst had passed. At the very least, they could chat safely across the kitchen table, right?

Wrong. More than a week later, another test finally sprouted a second line: bright, pink, positive. Five days after that, Hamilton was testing positive as well. This was his second bout of COVID since the start of the pandemic, and he wasn’t feeling so great. Congestion and fatigue aside, he was “just very frustrated,” he told me. He felt like they had done everything right. “If we have no idea if someone has COVID, how are we supposed to avoid it?” Now he has a different take on rapid tests: They aren’t guarantees. When he and his roommate return from their Christmas and New Year’s holidays, he said, they’ll steer clear of friends who show any symptoms whatsoever.

Hamilton and his roommate are just two of many who have been wronged by the rapid. Since the onset of Omicron, for one reason or another, false negatives seem to be popping up with greater frequency. That leaves people stuck trying to figure out when, and if, to bank on the simplest, easiest way to check one’s COVID status. At this point, even people who work in health care are throwing up their hands. Alex Meshkin, the CEO of the medical laboratory Flow Health, told me that he spent the first two years of the pandemic carefully masking in social situations and asking others to get tested before meeting with him. Then he came down with COVID shortly after visiting a friend who didn’t think that she was sick. Turns out, she’d only taken a rapid test. “That’s my wonderful personal experience,” Meshkin told me. His takeaway? “I don’t trust the antigen test at all.”

That might be a bit extreme. Rapid antigen tests still work, and we’ve known about the problem of delayed positivity for ages. In fact, the tests are about as good at picking up the SARS-CoV-2 virus now as they’ve ever been, Susan Butler-Wu, a clinical microbiologist at the University of Southern California’s Keck School of Medicine, told me. Their limit of detection––the lowest quantity of viral antigen that will register reliably as a positive result––didn’t really change as new variants emerged. At the same time, the Omicron variant and its offshoots seem to take longer, after the onset of infection, to accumulate that amount of virus in the nose, says Wilbur Lam, a professor of pediatrics and biomedical engineering at Emory University who is also one of the lead investigators assessing COVID diagnostic tests for the federal government. Lam told me that this delay, between getting sick and reaching the minimum detectable concentration of the viral antigen, could be contributing to the spate of false-negative results.

That problem isn’t likely to be solved anytime soon. The same basic technology behind COVID rapid tests, called “lateral flow,” has been around for years; it’s even used for standard pregnancy tests, Emily Landon, an infectious-disease physician at the University of Chicago, told me. Oliver Keppler, a virology researcher at the Ludwig Maximilian University of Munich who was involved in a study comparing the performance of rapid tests between variants, says there isn’t really a way to tweak the tests so that they’ll be any more sensitive to newer variants. “Conceptually, there’s little we can do.” In the meantime, he told me, we have to accept that “in the first one or two days of infection with Omicron, on average, antigen tests are very poor.”

Of course, Hamilton (and his roommate) would point out that the tests can fail even several days after symptoms start. That’s why he and others are feeling hesitant to trust them again. “It’s not just about the utility or accuracy of the test. It’s also about the willingness to even do the test,” Ng Qin Xiang, a resident in preventative medicine at Singapore General Hospital who was involved in a study examining the performance of rapid antigen tests, told me. “Even within my circle of friends, a lot of people, when they have respiratory symptoms, just stay home and rest,” he said. They just don’t see the point of testing.

Landon recently got COVID for the first time since the start of the pandemic. When her son came home with the virus, she decided to perform her own experiment. She kept track of her rapids, testing every 12 hours and even taking pictures for proof. Her symptoms started on a Friday night and her initial test was negative. So was Saturday morning’s. By Saturday evening, though, a faint line had begun to emerge, and the next morning—36 hours after symptom onset—the second line was dark. Her advice for those who want the most accurate result and don’t have as many tests to spare is to wait until you’ve had symptoms for two days before testing. And if you’ve been exposed, have symptoms, and only have one test? “You don’t even need to bother. You probably have COVID.”

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