COVID-19 Antigen Tests May Be Less Sensitive to Omicron: FDA

Megan Brooks

December 29, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Rapid antigen tests for COVID-19 might be less effective at detecting the Omicron variant that is spreading rapidly across the United States, according to the US Food and Drug Administration (FDA).

Early data suggest that COVID-19 antigen tests "do detect the omicron variant but may have reduced sensitivity," the FDA said in a statement posted December 28 on its website.

The FDA is working with the National Institutes of Health's Rapid Acceleration of Diagnostics (RADx) initiative to assess the performance of antigen tests with patient samples that have the Omicron variant.

The potential for antigen tests to be less sensitive for the Omicron variant emerged in tests using patient samples containing live virus, "which represents the best way to evaluate true test performance in the short-term," the FDA said.

Initial laboratory tests using heat-activated (killed) virus samples found that antigen tests were able to detect the Omicron variant.

"It is important to note that these laboratory data are not a replacement for clinical study evaluations using patient samples with live virus, which are ongoing. The FDA and RADx are continuing to further evaluate the performance of antigen tests using patient samples with live virus," the FDA said.

Testing Still Important

The agency continues to recommend use of antigen tests as directed in the authorized labeling and in accordance with the instructions included with the tests.

They note that antigen tests are generally less sensitive and less likely to pick up very early infections compared to molecular tests.

The FDA continues to recommend that an individual with a negative antigen test who has symptoms or a high likelihood of infection due to exposure follow up with a molecular test to determine if they have COVID-19.

An individual with a positive antigen test should self-isolate and seek follow-up care with a healthcare provider to determine the next steps.

The FDA, with partners and test developers, are continuing to evaluate test sensitivity, as well as the best timing and frequency of antigen testing.

The agency said that it will provide updated information and any needed recommendations when appropriate.

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