WASHINGTON — If you were exposed to COVID-19, take three home tests instead of two to make sure you’re not infected, according to new U.S. recommendations released Thursday.
Previously, the Food and Drug Administration had recommended taking two rapid antigen tests over two or three days to rule out infection. But the agency says new studies suggest the protocol may miss too many infections, and could lead to people spreading the coronavirus to others, especially if they don’t develop symptoms.
The new guidance applies to people without symptoms who think they may have been exposed. People with symptoms can continue to use two tests 48 hours apart.
Thursday’s update reflects the evolving understanding of the accuracy of antigen tests, which are less sensitive than laboratory tests but have become the standard testing method because of their speed and convenience. Instead of detecting the coronavirus itself, they detect protein traces, known as antigens, similar to rapid flu tests.
Health authorities have repeatedly warned that the tests can give false negative results if taken too soon. The Centers for Disease Control and Prevention recommends that people without symptoms wait five days after an exposure. That’s because it usually takes several days for the antigens to reach levels that can be detected via nasal swab testing.
All 22 home antigen tests on the U.S. market were authorized for emergency use based on preliminary data while companies and researchers gathered more definitive estimates of their accuracy.
The FDA said the latest decision reflects new information about the accuracy of antigen tests. In a government study, adding a third test improved accuracy from 62% to 79%.