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

US Food and Drug Administration make a new recommendation on Thursday that asymptomatic people using coronavirus antigen tests perform at least three tests, 48 ​​hours apart, to reduce infection missed rates.

According to the agency, people with Covid-19 symptoms should have at least two tests, 48 ​​hours apart.

The new guidelines come as Omicron’s highly contagious BA.5 subvariable continues to spread, and after the Centers for Disease Control and Prevention loosen its recommendation for periodic surveillance checks in most cases.

Many people have reported that home tests fail to detect their infection, but studies often indicate that rapid antigen testing also good at detecting Omicron when they discovered Delta, the previous variant was of interest.

Dr Michael Mina, a former Harvard epidemiologist who is now chief scientific officer of eMed, which sells home tests, said the new recommendations were “very sound”. “Sometimes it takes a virus two days to grow to a detectable level, and sometimes it takes six days to grow.”

Experts have long noted that rapid antigen tests, which are less sensitive than PCR tests, are designed for mass use and that they are more likely to detect coronavirus when people take them repeatedly. back in a few days.

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 highlight the importance of retesting after a negative test result to increase the chance of infection being detected,” said Dr. Director of the agency’s Center for Devices and Radiological Health, said in a statement.

New guidelines based on 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 by PCR testing between October 2021 and February of this year. .

It found that among those with symptoms, two tests taken 48 hours apart detected 93% of infections. But the same test model detected only 63% of infections in asymptomatic people.

When asymptomatic people took three tests, two days apart, the tests detected 79% of infections.

“We provide data-driven evidence on how to test using rapid antigen tests,” said Dr. Apurv Soni, assistant professor at UMass Chan School of Medicine, who led the study. “Testing schedules are important.”

The researchers said some study participants had Delta infections, while others had Omicron infections.

“The fact that tests can detect Omicrons is an important point that cannot be emphasized enough,” said Nathaniel Hafer, a molecular biologist at UMass Chan School of Medicine and an author of the study.

People who are worried that they may be infected even after receiving two or three negative results with home antigen tests can continue to test themselves, seek a more sensitive PCR test, or consult. doctor’s opinion, the FDA said.

The agency said that people who test positive at home should assume they have been infected and follow the guidelines set forth by the CDC.

CDC Updated Covid-19 guidance on Thursday but did not change the recommendation that people who test positive for coronavirus should isolate at home for at least five days.

The FDA says people don’t need to use the same brand of test every time.

“If you plan to use Covid-19 antigen tests at home, have several tests ready so you can test more than once,” the agency said.

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