Some 50% of people who test positive for Covid-19 on a rapid test after five days of infection are likely no longer contagious, a Journal of the American Medical Association study released on Wednesday suggests, after the Centers for Disease Control has received criticism from some experts for recommending a quarantine period of five days without using testing to determine when to end isolation.
All of those who tested negative for Covid with a rapid antigen test on day 6 of their infection—25% of study participants—had a negative viral culture, indicating they were likely no longer infectious and suggesting a negative rapid test could be a good way to confirm an end to isolation, researchers concluded.
But half of the three quarters of participants who tested positive for the coronavirus on a rapid test on day six of their infection also had a negative viral culture detected through a nasal and oral swab, according to the study, which researchers noted was limited by a small, mostly young and vaccinated sample group of 40 people.
The study comes several months after the CDC shortened the required quarantine period from ten days to five—with five days of mask-wearing—for those who are asymptomatic or have improving symptoms and suggested rapid tests on day 6 as an optional measure.
Imposing a universal negative rapid test requirement could “unduly extend isolation” for those who are no longer infectious, researchers concluded, though they noted proper mask-wearing and avoiding crowded venues for 10 days is key for those who could still be contagious.
The CDC has come under fire from some experts for its decision to shorten the quarantine period without a testing requirement, especially during an uptick in cases due to the highly transmissible omicron variant. Many experts say antigen tests—which are believed to be a better measure of infectiousness for those who are symptomatic because the tests are less sensitive than PCR tests—should be used as an additional precaution, while others have raised concerns the CDC’s guidance lacks clarity. Data from the United Kingdom shows roughly 31% of people remain infectious five days after their first positive Covid test, according to the CDC. The agency has defended its decision not to require testing to end quarantine, saying antigen tests have not yet been proven a good indicator of contagiousness after five days of infection and arguing people are much less likely to spread the virus after that period, especially while wearing a mask.
President Joe Biden, who first tested positive for Covid two weeks ago, waited for a negative Covid test to end isolation. After testing positive again for the coronavirus last week after completing a five-day course of the oral antiviral treatment Paxlovid—a phenomenon known as a “rebound” infection—Biden resumed isolation. People experiencing a rebound Covid infection may be capable of spreading the coronavirus to others, some research has found.