The U.S. Food and Drug Administration announced Tuesday that antigen COVID-19 tests, including the commonly used rapid, at-home tests, may not always accurately detect the Omicron variant.
“Early data suggests that antigen tests do detect the Omicron variant, but may have reduced sensitivity,” the FDA said in a statement issued Tuesday.
The update is based on preliminary results from a study of antigen tests, using patient samples with the Omicron variant, that the agency is conducting in conjunction with the National Institutes of Health (NIH). The FDA did not name specific tests that did or did not detect the Omicron variant.
“When you’re dealing with an antigen test, everyone knows from the beginning that it is not, by the nature of the technical aspect of the test, as sensitive as a PCR—so it isn’t 100% sensitive. But it has a considerable degree of usefulness in a number of different circumstances,” Dr. Anthony Fauci said Wednesday. In particular, antigen tests can be helpful in keeping children in school and college campuses safe.
“This is a heads-up that more details are coming and it will be very important to understand those details,” said Dr. Jessica Justman, associate professor of medicine in epidemiology at Columbia Mailman School of Public Health. At this point, she said, there are more questions than answers.
“Sensitivity is really not the only factor. What’s important from the perspective of outbreak control is how frequently you’re testing and the speed of reporting…so that you can quickly act on the results,” Justman told Fortune.
The FDA update comes about two weeks after Dr. Fauci noted that not all COVID tests are picking up Omicron infections. “We’re getting preliminary information that not all of the diagnostic tests will be accurate with Omicron,” the chief medical adviser to President Joe Biden said on Dec. 16.
What do less sensitive antigen tests mean for consumers?
For individuals who are concerned about the accuracy of their test results, Justman said it’s worth doing a test two days in a row if they can find several antigen tests: “If they do a rapid test two days in a row and are negative both times, that’s a way to handle that reduced sensitivity.”
In fact, many at-home antigen tests do already recommend testing at least twice on separate days. “If you are using the [antigen tests] serially, you are able to easily give up a little bit in terms of sensitivity,” Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention said Wednesday.
But antigen tests are not a silver bullet. For those who are feeling as if they may have COVID symptoms and their rapid antigen test comes back negative, Justman recommended treating it like a positive. “I would still start isolating, and I would go ahead and try to get another test,” she said. “I would not rely on a negative rapid test if you feel symptomatic.”
Think about it this way: If an otherwise healthy 18-year-old comes into an emergency room with chest pain, that person is probably not experiencing a heart attack. But if a 75-year-old-man comes into an emergency room with a history of diabetes and hypertension, and he has crushing chest pain, he probably is having a heart attack. It’s the same with COVID. Because the rate of COVID cases is quite high in most communities at the moment, it’s safer to assume you have it if you’re experiencing symptoms, Justman said.
Justman added that it’s not worth getting hung up on the brand of antigen tests until the FDA issues additional guidance. For now, as long as the test has been authorized by the FDA, consumers should use whatever brand they can find.
Beyond antigen tests
In addition to antigen tests, at-home PCR tests such as Labcorp’s Pixel or Vault’s are also available. But it’s worth noting that these require patients to mail the test to a lab and wait for results. Also, Labcorp is not currently taking Pixel orders through Jan. 2, 2022.
Vault, which has partnered directly with Minnesota, New Hampshire, and New Jersey to issue free testing to state residents, said its tests are detecting Omicron cases. “Vault Health’s tests can detect the presence of Omicron without additional sequencing,” a company spokesperson told Fortune. Vault helped detect the second known case in the U.S. through the company’s partnership with Minnesota.
Rapid at-home molecular tests are also available, but these can be expensive and may be harder to obtain. Cue COVID tests, for instance, retail for $474 for a three-pack of tests with a reader, and Lucira tests cost $89 for a single-use test kit.
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