These COVID Tests May Not Detect Omicron as Accurately, New Study Finds

The FDA has issued this urgent warning amid the new variant's spread.

Rapid COVID tests have been selling out in stores across the nation, with many retailers now limiting the number of tests customers can buy at one time. The increased demand comes as the new Omicron variant spreads quickly across the U.S. amid the busy holiday season—many virus experts are now urging even vaccinated individuals to test themselves immediately before gathering with others. But while at-home testing has increased significantly, health officials say data shows the new variant might be affecting the results.

RELATED: If You Have These 2 Symptoms, Get Tested for Omicron, Experts Warn.

On Dec. 28, the U.S. Food and Drug Administration (FDA) posted a statement warning that the Omicron variant might impact the accuracy of rapid antigen COVID tests. According to the agency, early data from preliminary studies by that National Institutes of Health's (NIH) Rapid Acceleration of Diagnostics initiative shows that these tests may be less capable of detecting the virus when it's caused by the new variant, due to its large number of mutations.

"Early data suggests that antigen tests do detect the Omicron variant, but may have reduced sensitivity," the FDA said, meaning that some people could receive a negative result despite being infected with COVID.

Rochelle Walensky, MD, the director of the Centers for Disease Control and Prevention (CDC), also recently questioned the accuracy of rapid testing for Omicron when discussing new isolation guidance from the CDC. The agency's updated guidelines say that people who test positive for COVID can leave isolation after five days (instead of 10) without testing again, provided they don't have symptoms.

"We opted not to have the rapid test for isolation because we actually don't know how our rapid tests perform and how well they predict whether you're transmissible during the end of disease," Walensky said in a Dec. 29 interview on CNN's New Day, noting that the CDC does recommend rapid testing during your initial exposure period.

But some experts have hit back at the both the FDA and the CDC's recent warnings. "CDC should have included negative antigen tests to end isolation. They didn't," Ashish Jha, MD, dean of Brown's School of Public Health, tweeted on Dec. 29. "Now some are justifying that decision by throwing antigen tests under the bus. Please don't do that. The long term cost of that messaging will be immense. Antigen tests are great when used properly."

Top White House COVID adviser Anthony Fauci, MD, also noted that the FDA has not advised individuals to stop using rapid tests. "What the FDA is saying today is that when you look at Omicron, its ability to detect Omicron, some of the tests have a diminution further of the sensitivity, but they still say the tests are useful and should be used," he said, per CBS Pittsburgh.

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For its part, the FDA said that it "continues to authorize the use of these tests as directed in the authorized labeling and individuals should continue to use them in accordance with the instructions included with the tests," adding that rapid antigen tests have always been known to be generally less sensitive and less likely to pick up earlier infections when compared to molecular PCR testing.

"With every new variant, we have to make sure that the tests work, and it looks like the tests work for this. But they're not picking up infections as early as previous versions," Gig Gronvall, PhD, a senior researcher at the Johns Hopkins Center for Health Security, told NBC News. "So if you feel any symptoms but test negative, it's not a get-out-of-jail-free card. You may need to test again and hold off a little bit on assuming that you're negative."

The FDA also advises that anyone who is experiencing symptoms or has a likelihood of infection due to exposure should follow a negative rapid test with PCR testing to determine whether or not they are actually infected.

RELATED: If You Have Omicron, This Is When You'll Begin to Feel Symptoms.

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