CDC last week reduced its isolation guidelines for people who test positive for Covid-19 to five days. Many health experts have pushed back on the guidelines, arguing that the shortened isolation period without producing a negative test could lead to more coronavirus transmission, and the agency on Tuesday updated its guidelines with a testing suggestion—but not a requirement.

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The controversy over CDC's updated Covid-19 isolation recommendations

According to CDC's updated recommendations, individuals who test positive for Covid-19 should isolate for five days instead of the previously recommended 10 days. After those five days, CDC said, "[i]f you have no symptoms or your symptoms are resolving … you can leave your house." However, CDC says individuals should still wear a mask until day 10. The recommendations are the same for vaccinated and unvaccinated individuals.

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According to CDC Director Rochelle Walensky, the change will help address potential economic and societal concerns. "With a really large anticipated number of cases [from omicron], we also want to make sure we can keep the critical functions of society open and operating," she said.

However, several health experts pushed back against CDC's updated guidelines, raising concerns about potentially infectious people leaving isolation too soon—particularly since the guidelines rely on individuals to assess their own transmission risk, NPR reports.

"To me, this feels honestly more about economics than about the science," said Yonatan Grad, an associate professor of immunology at the Harvard T.H. Chan School of Public Health. "I suspect what it will do is result in at least some people emerging from isolation more quickly, and so there'll be more opportunities for transmission and that of course will accelerate the spread of Covid-19."

Several experts have argued in favor of adding a testing requirement to CDC's isolation guidelines, which will allow people to more accurately gauge how infectious they are. "We should really be using objective concrete measures to decide whether somebody needs to continue being in isolation, such as rapid antigen testing," said Celine Gounder, an infectious disease specialist and epidemiologist at the NYU School of Medicine and Bellevue Hospital.

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In response to the criticism, CDC has defended its updated guidelines, citing "science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness," NPR reports.

According to a federal official who spoke to the New York Times, CDC partly based its updated guidance on unpublished modeling data on the spread of the delta variant that found the risk of viral transmission decreased to 13% after five days of testing positive.

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"We know that, let's call it 85%, of your transmissibility time is already behind you," Walensky said, speaking about CDC's reduced five-day isolation period. "A minority of it is in front of you. And if you wear a mask, you can avert it," she said.

Similarly, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said that "the likelihood of transmissibility is considerably lower in [the] second half of a 10-day period" which is why "CDC made the judgement that it would be relatively low risk to get people out."

CDC updates guidelines, but does not add testing requirement

Fauci on Sunday said CDC was considering adding a testing requirement to its isolation guidelines as an "extra layer of protection," The Hill reports. And on Tuesday, CDC issued updated guidance saying that those who have access to a Covid-19 test and want to take one should take an antigen test near the end of their five-day quarantine.

If their antigen test is positive, CDC said the infected person should keep quarantining until day 10. If the test comes back negative, the guidelines say the person is able to end isolation at day five but should continue wearing a well-fitting mask for an additional five days around people at home and in public.

"CDC's updated recommendations for isolation and quarantine balance what we know about the spread of the virus and the protection provided by vaccination and booster doses," Walensky said. "These updates ensure people can safely continue their daily lives."

But the updated guidance drew criticism from some health experts.

"I'm struggling to make heads or tails of it," said Megan Ranney, academic dean at the Brown University School of Public Health. "It's basically like 'get out of jail free at five days unless you happen to run into a rapid test in which case ….' It feels like a Rube Goldbergian contraption designed to confuse us all."

Experts argued the guidelines need to be simpler and clearer. "The newly updated [CDC] isolation guidance adds to the confusional state," Eric Topol, EVP of Scripps Research, said in a tweet.

"I'd recommend a rapid antigen test and if it's still positive, stay home longer," Ranney said. "And if you're symptomatic, you have to stay home until you get better." (Mueller, New York Times, 12/30/21; Huang, "Shots," NPR, 12/28/21; Hernandez, NPR, 1/2; Reyes, Axios, 1/2; AP/Modern Healthcare, 1/2; Choi, The Hill, 1/2; Schnell, The Hill, 1/2; Collins, CNN, 1/4; Franklin et al., NPR, 1/4; Mandavilli, New York Times, 1/4; Reed, Axios, 1/5; Weixel, The Hill, 1/4)