FDA says Covid-19 antigen tests may be less sensitive to Omicron variant, but they’re still an important tool

By Jen Christensen and Jamie Gumbrecht, CNN

The US Food and Drug Administration said Tuesday that quick antigen tests people take at home may be less sensitive to picking up the Omicron variant of the coronavirus, but health officials say they’re still a useful tool.

The FDA said its recent studies with the National Institutes of Health showed that although the antigen tests detected the Omicron variant, they did so with less sensitivity — meaning they’ll spot an infection less often.

The agency said it could not share any information on how much less sensitive any of the tests might be to the Omicron variant, but it is working to get more details.

“Studies are under way to confirm the reason for the apparent decreased sensitivity. Once that is known, adjustments to existing tests can be undertaken by each developer with support from the FDA, if appropriate,” the FDA told CNN in a statement.

Antigen tests are generally known to be less sensitive than PCR tests done in labs, but they are fast, more affordable and easy to perform at home.

The FDA suggests that people should continue to use these tests and make sure they follow the instructions closely. If someone tests negative with an antigen test but still suspects that they may have Covid-19 because they have symptoms or have been exposed to the coronavirus, they should follow up with a PCR (or molecular) test.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, encouraged people to continue to use rapid Covid-19 tests.

“The tests are still worthwhile. Don’t let anybody think that the FDA was saying that tests are no longer good. They say they’re less sensitive now. They never were 100% sensitive,” Fauci told CNN’s Michael Smerconish on Tuesday.

“What the FDA is saying today is that when you look at Omicron and 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.”

At a White House Covid-19 response briefing on Wednesday, US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky emphasized the importance of antigen tests in “places like test-to-stay to keep children in school, in higher ed to keep our college campuses safe.”

“If you’re using them serially, we are able to easily give up a little bit in terms of sensitivity,” she said.

Fauci said Wednesday that the FDA was aiming to be “totally transparent in saying the sensitivity might come down a bit, but they did emphasize there still is an important use of these tests.”

The lack of details drew criticism from some scientists and testing experts.

On Twitter, Dr. Michael Mina, chief science officer of eMed, criticized the FDA’s “exceedingly vague” statement that offered “no explanation or data.” He suggested it’s not that rapid tests are less sensitive “but simply that Omicron is more infectious.”

“It’s important for people to understand that ALL tests will falter on day 1. If you feel symptoms, regardless of the test type – ASSUME YOU ARE POSITIVE,” he wrote. “But also recognize that the tests will still detect Omicron but know they may fumble on day 1.”

In its announcement on Tuesday, the FDA did not identify specific tests that might have reduced sensitivity.

Abbott, a company that makes a popular home antigen test, told CNN that it is watching the situation with the Omicron variant closely and has not seen a change in the performance of the BinaxNOW test.

“Abbott has been intently monitoring the mutations of COVID-19 so we can ensure our tests can detect them. We’ve conducted lab analyses and tests on the omicron variant from live virus, including from the first U.S. Omicron case, and BinaxNOW detected the virus in all tests we performed at equivalent sensitivity as other variants. Additionally, our data from customer use has not shown any change in test performance,” it said in a statement to CNN.

“We know our tests are a critical tool in controlling spread of the virus and we will remain vigilant in conducting analyses and closely monitoring test performance.”

President Joe Biden acknowledged this week that the US hadn’t pushed enough to scale up Covid-19 testing capacity. Now, holiday demand and the highly transmissible Omicron and Delta variants are leading to empty store shelves and long lines at testing sites.

The administration is working to distribute half a billion free at-home tests, but it’s not clear when those tests will reach Americans who want them.

White House Covid-19 Response Director Jeff Zients said Wednesday that the administration expects the contract for purchasing the 500 million at-home rapid tests “to be completed late next week,” adding that the Departments of Health and Human Services and Defense “are executing on an accelerated contracting timeline” to speed up distribution.

“That means that the first deliveries from manufacturers will start in January. We’ll set up a free and easy system, including a new website, to get these tests out to Americans,” Zients told CNN’s Jeremy Diamond during the White House briefing. “We’re actively working to finalize that distribution mechanism, which includes a website where people will be able to order tests for free, and we’ll share more details in the weeks ahead — days and weeks ahead.”

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CNN’s Donald Judd and Maggie Fox contributed to this report.