The Food and Drug Administration said on Tuesday that rapid antigen tests may be less sensitive at detecting the highly infectious omicron variant and result in a “false negative.”
Preliminary research by the FDA, in collaboration with the National Institutes of Health’s Rapid Acceleration of Diagnostics Program, used samples from patients confirmed to be infected with the Omicron strain of the virus, known as “antigens,” to study the performance of home tests. ” also known as. “testing.
The agency said early data suggests that antigen tests “detect the oomicron variant, but sensitivity may be low,” meaning it’s possible such tests could miss infections.
Previous testing by RADX focused on heat-inactivated virus samples, which are patient samples confirmed to be infected with the Omicron variant who have been heat-treated so that the virus no longer survives. Currently available antigen tests were able to detect the mutated strain “with similar performance” to the other variants in that study. But, the agency noted that while live virus is the best way to evaluate true test performance, “heat-inactivated samples are the best available option when samples from a patient with live virus are not available.”
The FDA stopped short of asking people to avoid using antigen tests and did not specify the brands of tests used in the study. The agency also emphasized that the findings are based on laboratory data, not more reliable clinical study evaluations, which are currently underway.
“The FDA continues to authorize the use of these tests as directed in the authorized labeling and individuals should continue to use them in accordance with the instructions included in the tests,” the agency said in a statement. “Antigen tests are generally less sensitive and less likely to pick up infection very quickly than molecular tests.”
The new findings come at a time when case numbers are rising across the country, at a time when family and friends want to gather over the holidays, due to long lines for PCR tests to diagnose infections over-the-counter. Over the counter antigen tests – which are better at detecting low levels of the virus – and delaying the turnaround time for their lab results.
But, the CDC said on Wednesday that less than 1% of the genetically sequenced US COVID-19 cases last week were omicron variants; The delta variant accounted for more than 99%, reducing concerns about currently authorized antigen tests that do not result in infection. It comes a day after the agency significantly lowered estimates for the percentage of new cases linked to the Omron version.
The CDC previously reported that the Omron version covered 73% of all cases for the week of December 18. But on Tuesday, the agency revised that number up to 22.5%, suggesting that while the new version was on the rise, delta – which is under more severe stress – is still a driving force behind the current surge. The most recent report estimated that as of December 25, 59% of all US infections were due to omicrons, a figure that will likely be revised as more data is processed from genetic sequencing.
Rapid antigen tests, which work by detecting surface proteins of the coronavirus, are relatively cheap and quick, with results known in about 15 minutes. However, they may miss the early stages of the COVID-19 infection. The most popular home tests recommend users to do two tests on different days to ensure more accurate results.
In an interview with NBC’s “Today” show, CDC director Dr. Rochelle Welsonki said that while the antigen test may not perform as well as it did for other types, “it still raises a lot of infections.” is” and the agency encourages its use.
“They’re really really helpful tools,” Valensky said. “But what we will reiterate, and also our guidance is that if you have a negative antigen test and you have symptoms, you should go ahead and get a PCR test. And those antigen tests are really helpful for things like testing.” to be in school, where we’re getting an antigen test done every day, or every other day, or where they’re using them to screen students every several days in higher education, where they’re really They perform very well.”
The FDA recommends that if a person tests negative on an antigen test but has symptoms of COVID-19 or a “high probability of infection due to exposure,” they should undergo a molecular PCR test to confirm the result. Follow up action should be taken. The agency said a person who tests positive with an antigen test should self-isolate and seek follow-up care with a health care provider to determine next steps.
Earlier this month, the White House announced that the Biden administration would distribute 500 million rapid COVID-19 tests for free to American families starting in January.
As cases continue to rise in many parts of the country due to the spread of the Omicron version of the coronavirus, the CDC has changed its guidelines for when vaccinated and unvaccinated people can return to work after exposure. LX News Now host Eric Alvarez explains why the change was made and what you need to know.