Rapid COVID-19 tests are worse at detecting Omicron, FDA says, citing new lab data

• The FDA said rapid antigen tests appeared less sensitive against Omicron, citing early lab studies.
• Rapid tests are generally less accurate than PCR tests.

Rapid antigen tests appear less sensitive to Omicron than previous variants, the Food and Drug Administration said Tuesday.

"Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity," the FDA said.

The statement is based on laboratory findings, which are generally less dependable than clinical-trial results.

But because clinical trials take a lot longer, laboratory findings are the "best way to evaluate true test performance in the short-term," the FDA said.

People can still use the rapid tests — which are cheaper and more convenient — but should be aware of their shortcomings, the FDA said.

A follow-up PCR test is much more reliable and should be used by people who have symptoms or know they have been exposed to the coronavirus, the FDA added.

The news came as the White House prepared to distribute 500,000 free rapid COVID-19 tests and make over-the-counter kits free starting in January.

How well rapid tests perform against Omicron has been debated widely as the new variant has surged around the world.

The UK Health Security Agency previously said there was "no change in performance" of these tests against Omicron. This was also the position held by the FDA one week ago.

The latest run of experiments changed the agency's mind. In that batch, the FDA used live virus taken from patient samples, which is a good proxy for what is happening in the real world.

"Although the data is preliminary, the FDA believes it is important to share with the public," Stephanie Caccomo, an FDA spokesperson, told Politico. "We will continue to keep the public informed if additional information comes to light."

Abbott, one of the main providers of rapid tests in the US, contacted Insider to dispute the FDA findings.

John M. Koval, a spokesperson for the company, said Abbott's lab analysis and customer data showed that its tests worked as well for Omicron as for other variants.

Koval pointed to a Twitter thread posted by the epidemiologist Michael Mina, who said that the tests were not at fault.

Instead, Mina said Omicron appeared harder to spot with tests because it caused more infection with less virus in the lab. This, he said, would be hard for any test to find.

Rapid tests are generally less sensitive

Even before Omicron emerged, rapid tests were known to be hit or miss.

One review found that these tests were 58% accurate for those who didn't have symptoms and 72% accurate for those who did, Insider previously reported.

Timing of testing is also crucial, as it takes a couple of days for the virus to spread enough in the body to be picked up by a test, Insider's Hilary Brueck and Shayanne Gal previously reported.

The best bet, according to available data, is to take several rapid tests over a few days and test hours, not days, before mixing with others, experts previously told Insider.

That might be even more true for Omicron, given the latest data, which suggests that the viral load required to trigger an antigen test is higher with the variant than with others.

Masking is still recommended in social settings, especially since vaccinated people seem more likely to carry Omicron than previous variants, according to the CDC.