Why health experts still back at-home antigen tests after FDA pegs them 'less sensitive' to omicron

Dr. Fauci says if you want the most accurate results, you should take a PCR test.
SAN JOSE, Calif. (KGO) -- New rapid at-home tests could be at stores soon, after the FDA approved two additional brands.

However, there are questions about how effective those antigen tests are at detecting the omicron variant.

We are just days away from the New Year and many are still on the hunt, hoping to get their hands on a quick at-home antigen test. That demand has now been met with a new FDA discovery.

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The agency found that while antigen tests detected the omicron variant, they did so with "less sensitivity," finding it's possible such tests could miss an infection.

"They never have been 100% sensitive," Dr. Anthony Fauci told ABC News. "If you want to definitively find out if someone is infected- for example, if someone has symptoms and has reason to believe they're infected, the test to use is a PCR test."

Lab-based PCR tests are more sensitive and have a turnaround time of up to 72-hours.

Dr. Fauci said although sensitivity is somewhat diminished with antigen tests, they're still a useful tool for broad surveillance.

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UCSF Epidemiologist Dr. George Rutherford said antigen tests are reliable with no variant-to-variant variability.

"The tricky part is just timing," Dr. Rutherford said. "And omicron, may have a shorter incubation period than the prior variants. And that's one of the reasons that the isolation period has gotten shrunk down."

Rapid antigen tests are relatively inexpensive and offer results in about 15 minutes. They work by detecting surface proteins of the coronavirus.

Most popular self-tests tell people to take two tests on separate days for more accurate results.

"The bottom line is that these are very reliable tests. They're testing for exactly the same thing- for every strain, there's no variant-to-variant variability," Dr. Rutherford added. "They're looking at individual proteins that don't have anything to do with where the mutations are."

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ABC7 News Special Correspondent Dr. Alok Patel said, "An antigen test - if you can get your hands on one - should be taken right before a potential gathering where you're going to see people. That's like a snapshot in time."

"You want to take it right before you walk in the door of a gathering," he added.

On Wednesday, came word of two new over the counter at-home antigen tests, authorized by the FDA.

One test is manufactured by SD Biosensor and distributed by Roche. It was authorized on December 24.

The other test is the Siemens. It was authorized on December 29.

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The US Department of Health and Human Services said the authorizations will bring tens-of-millions of new tests per month, across the country.

"This is the time for more testing, not less testing," said Dr. Rutherford.

The FDA says "studies are underway" to understand why the Omicron variant might impact rapid tests.

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