If you're taking an at-home COVID-19 test and want to be confident you're clear of the virus, you'll need not just one or two but three tests with negative results over five days before it's likely safe to hug grandma.
That's the new recommendation issued Thursday by the Food and Drug Administration. It follows a new study that concludes using three home COVID tests with 48 hours between tests for those without symptoms delivers a higher degree of accuracy than two tests over three days.
The recommendation for a third test is directed at those who fear they may have been exposed to the virus or want to leave no doubt about their negative status.
Even with that stipulation, Thursday's recommendation signals a significant shift in a system where home tests are mostly sold and distributed in two-test kits.
Home antigen tests are quick and inexpensive but less sensitive than polymerase chain reaction or PCR tests, which are usually performed in a lab. While the FDA has cleared more than two dozen home antigen tests that detect proteins from the COVID-19 virus, it says the home tests are less accurate, especially in detecting a case early in an infection or in people who don't have symptoms.
That means people who have no symptoms and take a home test immediately after being exposed to the virus could get a false negative result. That's why the FDA had been recommending repeat testing, usually over 48 hours.
The new study, led by University of Massachusetts researchers, said the two-test kits typically sold at pharmacies or grocers are still highly accurate for people with symptoms. Study participants with symptoms who used home tests twice over 48 hours accurately detected COVID in 93% of cases in which the virus was found using more sensitive labs tests.
Yet among people who weren't showing symptoms, the accuracy fell to 63% for those who took two tests over 48 hours. Taking a third test two days after the second improved the accuracy to 79%.
The study drew more than 5,000 participants from a larger federal study funded by the National Institutes of Health. Participants tested themselves every 48 hours for 15 days using home tests. They also collected samples that were sent to a lab for comparative PCR testing.
Researchers said the higher sensitivity of using three tests over five days could catch more cases and inform infected people without symptoms to avoid contact with others, limiting spread.
"This was the type of data needed to instill confidence in antigen testing," said Dr. Apurv Soni, a UMass Chan Medical School assistant professor of medicine and a principal investigator on the study.
The study shows antigen testing works for those with or without symptoms, Soni said, but the key is communicating the right message. People without symptoms should take three tests with 48 hours lapsed between each test to be more certain they don't carry the virus.
Soni acknowledges it's "not a trivial change" to recommend three tests for people without symptoms. "Companies would have to decide what makes sense from a product (packaging) perspective," Soni said.
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The Biden administration has required private health insurers and Medicare to cover a monthly allotment of four boxes containing two tests apiece. The administration also has allowed Americans to order three rounds of home tests through the government-run website CovidTests.gov; the free test kits are delivered to a person's home address by the U.S. Postal Service.
Private insurers and Medicare must pay the cost of testing through the duration of the public health emergency, which has been extended through at least mid-October.
Officials with QuidelOrtho, which markets the QuickVue home COVID test, said the study shows serial testing is effective.
"The UMass study adds important data that will be closely examined," said Douglas Bryant, chairman and CEO of QuidelOrtho. "The key takeaway is that serial testing remains an effective tool for both symptomatic diagnosis and asymptomatic screening."
This article originally appeared on USA TODAY: COVID fears? FDA now says you need to pass 3 home tests to be safe