Dec. 30, 2021 -- Rapid COVID-19 tests used at home are less sensitive to the Omicron variant than they are to other strains of the virus, the U.S. Food and Drug Administration says.

The FDA, working with the National Institutes of Health, looked at how the rapid tests, also known as antigen tests, reacted to confirmed Omicron samples from patients, the FDA said in a statement.

“Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity,” the FDA said, meaning the rapid tests sometimes give false negatives.

With COVID case counts climbing because of the surging Omicron variant, the home kits have been in great demand, with many pharmacies selling out quickly. The rapid tests are self-administered and give a faster result than a molecular (PCR) test, which must be processed in a laboratory. However, they are less accurate than the PCR tests.

The FDA did not recommend people stop using the home tests.

“The FDA 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,” the FDA statement said. “Antigen tests are generally less sensitive and less likely to pick up very early infections compared to molecular tests.”

The scientist leading the NIH RADx (Rapid Acceleration of Testing) program warned Americans should not abandon using rapid tests based on the announcement. Dr. Bruce Tromberg told ABC News, “The tests are an essential component of what we need, especially in the time of very rapidly expanding omicron."

The FDA said a person who tests negative with an antigen test should follow up with a PCR test if they have COVID symptoms or have been exposed to an infected person. A person who tests positive with an antigen test should self-isolate and seek follow-up care with a health care provider.

Gigi Gronvall, a senior researcher at the Johns Hopkins Center for Health Security, told NBC News that the FDA statement confirms how quickly COVID is evolving.

“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,” she said. “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 said previous testing of the home kits used heat-inactivated virus samples instead of the live virus. The new testing noticed the drop off in sensitivity.

The Biden administration announced last week that it would distribute 500 million antigen home test kits for free to Americans.

Show Sources

FDA. “SARS-CoV-2 Viral Mutations: Impact on COVID-19 Tests”

NBC News: “FDA says rapid Covid antigen tests may be less sensitive in detecting omicron”

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