The Abbott BinaxNOW, a widely used at-home coronavirus test, can detect most people who are infected with the new Omicron variant and are carrying high levels of the virus, according to a new, real-world study of more than 700 people who visited a walk-up testing site in San Francisco.
Like all rapid antigen tests, BinaxNOW is less sensitive than P.C.R. tests, which can find even very small traces of the virus, and federal health officials have recently sent mixed messages about the usefulness of such antigen tests. But they have generally been good at catching people who have high viral loads and are most likely to be infectious.
The new study, which has not yet been reviewed by experts, found that overall the BinaxNOW detected 65 percent of the infections identified via P.C.R. testing, but 95 percent of people who had the highest viral loads. Among those with high levels of the virus, the tests caught 98 percent of those with symptoms and 90 percent of those without symptoms, the researchers found.
The test’s performance was roughly on par with what the scientists had observed in real-world studies before Omicron emerged, they said.
“It’s working as it was designed,” said Joseph DeRisi, a biochemist at the University of California, San Francisco, who is a president of the Chan Zuckerberg Biohub and an author of the paper. “There does not seem to be any performance deficit with Omicron.”
The findings come after some preliminary studies raised questions about whether rapid antigen tests might be less sensitive for Omicron than for other variants — and whether saliva samples might be a better way to detect the variant than the nasal swabs currently used in antigen tests.
At a Senate hearing on the federal coronavirus response on Tuesday, Dr. Janet Woodcock, the acting commissioner of the Food and Drug Administration, said that scientists were still trying to determine how well the currently authorized at-home tests work for the new variant.
“We believe all of them detect Omicron,” she said. “We simply feel they are somewhat less sensitive than they were to some of the previous variants.”
The new research, which relied on nasal swabs, does not address how early in the course of an infection the antigen tests can detect the variant, as one small previous study did, or whether the tests would perform better with saliva samples. And the results cannot be extrapolated to other antigen tests, which must be evaluated individually, the researchers cautioned.
But they suggest that BinaxNOW should still be able to pick up most infectious Omicron cases.
“This tool continues to be very important,” said Dr. Diane Havlir, an infectious disease physician specialist at the University of California, San Francisco, and an author of the paper.
The new study, conducted on Jan. 3 and 4, was performed independently of Abbott, she noted, although the company did provide BinaxNOW test kits for a prior study, in 2020. The test kits for the new study were provided by the health department, she said.
Because the tests may not catch people who have been infected very recently, the researchers recommend that people who are exposed to the virus then test more than once over a period of a few days.