The Food and Drug Administration on Tuesday advised that while rapid antigen tests can still detect the omicron variant of COVID-19, they might have “reduced sensitivity” to the viral strain sweeping the nation. 

What You Need To Know

  • The FDA on Tuesday advised that while rapid antigen tests can still detect the omicron variant of COVID-19, they might have “reduced sensitivity” to the viral strain

  • Because of omicron's numerous mutations, early data has suggested the variant could potentially evade detection by some tests 

  • The FDA said that “overall test sensitivity should not be impacted,” as most antigen tests detect numerous genetic targets 

  • In its advisory, the FDA noted that at least one rapid PCR test – Applied DNA Sciences’ Linea COVID-19 Assay Kit – will fail to detect the omicron variant

While scientists are still studying aspects of the omicron variant, federal health officials maintain it has “many concerning spike protein substitutions,” some of which might indicate resistance to vaccines and therapeutics, as with previous strains. 

Because of omicron's numerous mutations, early data has suggested omicron could potentially evade detection by some tests depending on the type of test used, the specific protein sequence in individual cases and proper use of the tests. 

“The update includes preliminary study results of some antigen tests using patient samples containing live virus,” the FDA wrote in part. “Early data suggest that antigen tests do detect the omicron variant but may have reduced sensitivity.”

The data comes from a collaboration with the National Institutes of Health's (NIH) RADx program, which aims to speed production of point-of-care tests. 

Antigen tests detect multiple genetic targets, two of which – the N-gene and S-gene – can be reduced in the omicron variant, but not so in the delta strain. While the deletion or decreased sensitivity of one of the genetic targets does not necessarily indicate the presence of a specific strain, said specimens “may be omicron variants and should be prioritized for sequencing confirmation,” per the FDA.

Antigen tests that show one of the gene changes can be useful in identifying different variants, but can also lead to the potential for false positives should the test fail to detect the mutations.

Still, the FDA said that “overall test sensitivity should not be impacted,” as most antigen tests detect numerous genetic targets and require serial testing for more accurate results.

In an interview with ABC's "Good Morning America" on Wednesday, CDC Director Rochelle Walensky said that rapid antigen tests can "absolutely" still be trusted.

"We do know that the most sensitive test that you can do is a PCR test," Dr. Walensky explained. "So if you have symptoms, and you have a negative antigen test, then we do ask you to go and get a PCR to make sure that those symptoms are not attributable to COVID."

"But those antigen tests still work quite well," she continued. "And they work well especially in places that we're using them, like in higher education, in tests to stay in schools, where we're doing several tests, one every other day, every third day, and that's really when they work well as well."

"We still are encouraging their use," Dr. Walensky added, but warned that those tests "may not work as well as they had for the delta variant."

The FDA also found that at least one rapid PCR test – Applied DNA Sciences’ Linea COVID-19 Assay Kit – will fail to detect the omicron variant due to deletions at certain amino acid positions and mutations at nucleotide positions.

“The two viral targets of this test cover the portions of the S-gene where these mutations occur,” the FDA wrote in part, adding that the agency is continuing to “gather additional information and work with the manufacturer to address this issue.”

There are a few key differences between PCR and antigen tests. PCR tests, which detect genetic material of the virus, are sent to a lab for analysis, and can typically more accurately detect asymptomatic COVID. Rapid antigen tests can be used at home, and are better suited for individuals already showing symptoms.