People exposed to Covid may need to take up to three home tests, FDA says

The U.S. Food and Drug Administration issued a new recommendation on Thursday that asymptomatic people using home Covid-19 antigen tests take at least three tests, each spaced 48 hours apart, to reduce the chances of missing an infection. .

People who show symptoms of Covid-19 should take at least two tests, 48 ​​hours apart, according to the agency.

The new guidelines come as the highly transmissible BA.5 subvariant of Omicron continues to spread and after the Centers for Disease Control and Prevention relaxed its recommendation for routine surveillance testing in most circumstances.

Many people have reported that home tests have failed to detect their infections, but studies have generally shown that rapid antigen tests are as good at detecting Omicron as they were at detecting Delta, the previous variant. worrying.

Experts have long noted that rapid antigen tests, which are less sensitive than PCR tests, are designed to be used in series and are more likely to detect coronavirus when people take them repeatedly over several days. .

But the new recommendations underscore the need for “additional testing over a longer period of time,” the agency said.

“New FDA recommendations for home Covid-19 antigen testing highlight the importance of repeat testing after a negative test result to increase the chance 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, which has yet to be 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 using PCR tests between October 2021 and February this year.

It found that among symptomatic people, two tests taken 48 hours apart detected 93% of infections. But the same testing regimen detected only 63% of infections in asymptomatic people.

When people without symptoms took three tests, each two days apart, the tests detected 79% of infections.

The findings suggest that “serial testing with antigen tests remains a useful way to detect infection,” Nathaniel Hafer, a molecular biologist at UMass Chan Medical School and study author, said in a statement.

People who fear infection even after receiving two or three negative home antigen test results can continue to test themselves, seek out a more sensitive PCR test, or seek medical attention, the FDA said.

Those who test positive using home tests, the agency said, 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 isolate themselves at home for at least five days.

People don’t need to use the same test brand every time, the FDA said.

“If you plan to use home COVID-19 antigen tests, have multiple tests on hand so you can test more than once,” the agency said.

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