The U.S. Food and Drug Administration on Thursday issued a new recommendation that asymptomatic people taking home Covid-19 antigen testing do at least three tests, 48 hours apart, to reduce the chance of contracting an infection is overlooked.
People with Covid-19 symptoms should have 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 relaxed its recommendation for routine surveillance testing in most cases.
Many people have reported that home testing failed to detect their infections, but studies have generally shown that rapid antigen tests are just as good at detecting Omicron as they are at detecting Delta, the earlier concern variant.
Experts have long noted that rapid antigen tests, which are less sensitive than PCR tests, are designed for serial use and are most likely to detect the coronavirus when people take them repeatedly over several days.
But the new recommendations emphasize the need for “additional testing over a longer period of time,” the agency said.
“The 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 infection,” said Dr. Jeff Shuren, director of the agency’s Center for Devices and Radiological Health, said in a statement.
The new guidelines are based on the results of a new national study that 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 with PCR tests between October 2021 and February this year.
It found that in symptomatic people, two tests taken 48 hours apart detected 93 percent of infections. But the same test pattern only detected 63 percent of infections in asymptomatic people.
When people without symptoms took three tests two days apart, the tests caught 79 percent of the infections.
The results suggest that “batch testing with antigen tests remains a useful way to detect infection,” Nathaniel Hafer, a molecular biologist at UMass Chan Medical School and author of the study, said in a statement.
People who worry they may be infected even after getting two or three negative results on at-home antigen tests can continue to test themselves, seek a more sensitive PCR test, or consult a doctor, the FDA said.
Those who test positive with home testing should assume they are infected and follow guidelines set by the CDC
The CDC updated its Covid-19 guidance on Thursday but did not change its recommendation that people who test positive for the coronavirus should isolate at home for at least five days.
People don’t have to use the same test brand every time, the FDA said.
“If you plan to use COVID-19 antigen testing at home, have multiple tests on hand so you can test more than once,” the agency said.