Aug. 11, 2022 – It might be a good time to stock up on home COVID-19 tests.
Today, the FDA issued new guidance on at-home COVID testing. It still recommends repeat testing after a negative result, but is also recommending that people who have no symptoms but think they have been exposed take three tests instead of two.
The new guidance says:
- If a first or repeat test is positive, follow the CDC guidance on isolation and get medical care.
- If the first test is negative and you have symptoms, test again 48 hours later. You may choose to test yet again 48 hours after the second test, and may also consider getting a laboratory molecular-based (PCR) test and seeking medical care.
- If the first test is negative, you don’t have symptoms, but you believe you have been exposed, test again 48 hours later, then 48 hours after the second negative, for a total of at least three tests. After three negative tests, if you are concerned, the FDA suggests testing again at home, getting a PCR test, or getting medical advice.
Current guidelines from the CDC recommend testing at home right away if you get symptoms. If you have been exposed to COVID-19, it recommends testing at least 5 days after exposure – and if that test is negative, it says to consider testing again 1-2 days later.
The new guidance from the FDA is based on findings from a new study by University of Massachusetts Chan Medical School researchers showed the new timelines are more likely to detect an infection.
Researchers evaluated 5,609 people who are enrolled in the national Test Us At Home study, from October 2021 to January. The participants used one of three retail test kits and also collected a sample for a molecular PCR test. They tested every 48 hours for 15 days.
During the study period, 154 people tested positive for the coronavirus that causes COVID-19, based on the PCR samples. After testing twice at home over 48 hours, more than 90% of infections were detected in symptomatic people who began testing within the first week.
Serial testing three times with an at-home test at 48-hour intervals detected more than 75% of infections, an increase from about 60% after testing just twice.
The study is published as a preprint and is not yet peer-reviewed.
More on the Study
Bottom line from the study: At-home antigen tests are more likely to detect COVID-19 within the first week of infection if a person who doesn’t have symptoms tests three times, with 48 hours in between each test, and people with symptoms test twice, with the one 48-hour interval.
“Antigen tests work as long as people use them as indicated,” says Apurv Soni, MD, an assistant professor of medicine at UMass and the study’s principal investigator. “The problem is, the research on how to use home tests has been squishy.”
His team set out to find out how well the home tests could detect SARS-CoV-2, the virus that causes COVID-19, for people with and without symptoms.
The analysis included only people who had no symptoms and tested negative by both at-home antigen and PCR tests on the first day of the study. The home tests used in the study were Quidel’s QuickVUE At-Home; Abbott’s BinaxNOW; and Becton, Dickinson and Company’s BD Veritor.
For those with symptoms who tested negative twice, those two tests found about 94% of the infections, Soni says. But “if you are asymptomatic, you have to do three tests 48 hours apart to capture 79% of the infections.”
The FDA’s new safety communication is based on the study finding that when those without symptoms test just twice, many infections go undiscovered, making it easy to spread the infection to others.
Those without symptoms may simply not have enough virus in their body to get a positive test at first, says Carly Herbert, an MD/PhD candidate at UMass Chan Medical School, one of the study co-authors. “The rapid antigen test is very correlated with viral load. That may be why it takes that long.”
The study was supported by the National Institutes of Health Rapid Acceleration of Diagnostics Tech program.
Real-World Logistics
Translating advice about when and how to do home tests to real-world situations isn’t simple, Soni says, especially for those who don’t have symptoms.
If someone goes to a party and then has symptoms, they could start testing then, and repeat the test twice, he says. If both are negative, there’s a 94% chance they don’t have COVID, according to the UMass study.
“If you don’t have symptoms, do three tests 48 hours apart sometime after you find out you were exposed,” Soni says, acknowledging that the notification time varies.
His team is reviewing data from their research on those details, as well as ideal timelines, and hopes to have more information soon, he says.
Infectious Disease Doctors Weigh In
The study looked at a question that needs addressing, says William Schaffner, MD, a professor of preventive medicine and infectious disease specialist at Vanderbilt University Medical Center. “A lot of people see that one negative test as a ‘Get out of jail free card.’”
What the researchers have found is that “with the development of time, you are more likely to test positive,” he says.
Biological differences between COVID-19 variants may explain differences in testing and failure to pick up an infection on the first test, says Wilbur Lam, MD, PhD, a professor at Emory University and the Georgia Institute of Technology. The rapid tests, compared to traditional PCR tests, seem “to be less sensitive, with false negatives, especially in the first few days of infection.” Testing serially improves that sensitivity, he says.
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The study data is solid, Schaffner says. But with advice to test more, public officials are going to have to supply more tests if they hope people will comply, he says.
Will people follow the new advice? “There will be a segment of the population that will follow this” closely, Schaffner says. “But the large majority of the people are not going to be interested in repeated testing.” Even so, “the study results make good sense,” he says.
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