The U.S. Food and Drug Administration issued a new recommendation on Thursday that asymptomatic people taking Covid-19 antigen testing at home should have at least three tests, each spaced 48 hours apart, to reduce the chance of missing an infection. .
People with Covid-19 symptoms should undergo at least two tests, 48 hours apart, according to the agency.
The new guidelines come as Omicron’s highly transmissible BA.5 subvariant continues to spread, and after the Centers for Disease Control and Prevention relax their recommendation for routine surveillance testing in most circumstances.
Many people have reported that home tests failed to detect their infections, but studies have generally shown that rapid antigen tests are just as good at detecting Omicron as they were at detecting Delta, the previous variant of concern.
Experts have long noted that rapid antigen tests, which are less sensitive than PCR tests, are designed to be used serially, and are most likely to detect coronavirus when people take them repeatedly over the course of several days.
But the new recommendations emphasize the need for “additional testing over a longer period of time,” the agency said.
“FDA’s new recommendations for at-home Covid-19 antigen testing underscore the importance of repeat testing after a negative test result to increase the likelihood of detecting an infection,” Dr. Jeff Shuren, the director of the agency’s Center for Devices and Radiological Health, said in a statement.
The new guideline is based on the results of a new national study, which has not yet been published in a scientific journal. The study, led by researchers at the University of Massachusetts Chan Medical School, focused on 154 people who tested positive for the virus between October 2021 and February this year using PCR tests.
It found that among symptomatic people, 93 percent of infections were detected by two tests 48 hours apart. But the same test pattern detected only 63 percent of infections in asymptomatic people.
When people without symptoms took three tests, each two days apart, the tests caught 79 percent of the infections.
The results suggest that “serial antigen testing continues to be a useful way to detect infection,” Nathaniel Hafer, a molecular biologist at UMass Chan Medical School and an author of the study, said in a statement.
People who fear they may be infected even after receiving two or three negative results on home antigen tests can continue to test themselves, seek a more sensitive PCR test or see a doctor, the FDA said.
Those who test positive using home tests, the agency said, should assume they are infected and follow guidelines set forth by the CDC
The CDC updated its Covid-19 guidelines on Thursday, but hasn’t changed its recommendation that people who test positive for the coronavirus be isolated at home for at least five days.
People don’t have to use the same brand of test every time, the FDA said.
“If you plan to use COVID-19 antigen testing at home, have several tests on hand so you can test more than once,” the agency said.