Federal health officials’ decision to shorten isolation periods for Americans infected with the coronavirus received both moderate support and fierce opposition from scientists on Tuesday, most notably over the lack of a testing requirement and fears that omitting the spread of the highly contagious Omicron could accelerate variant.
The new guidance, which came amid a flurry of new infections that has starved many workers’ hospitals, seemed to some scientists a necessary step to bolster the workforce in vital industries. And encouraging people to come out of isolation early after they test negative could save them the rigors of extended periods at home.
But dropping hundreds of thousands of infected people from those tests — even if, crucially, their symptoms haven’t completely gone away — risks seeding new cases and putting even more strain on already overburdened health systems, experts said in interviews on Tuesday.
“To me, this is honestly more about economics than science,” said Yonatan Grad, an associate professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, who has tracked coronavirus infections in the National Basketball Association.
“I suspect what it will do is at least some people will come out of isolation faster, and so there will be more opportunities for transmission and that will of course accelerate the spread of Covid-19,” he added. noted that people were unlikely to strictly adhere to masking advice after leaving isolation.
dr. Rochelle P. Walensky, director of the Centers for Disease Control and Prevention, said in an interview Tuesday that the new guideline was necessary because of the large number of people on the brink of becoming infected.
In a series of holiday weekend meetings, she said, agency officials pored over portability data for past variants and signs that Omicron was causing less serious illness. But in the end, Dr. Walensky said, she decided rapid tests weren’t effective enough to diagnose infectiousness in humans.
“You don’t necessarily have to take a test if you don’t know what you’re going to do with the result,” she said, adding: “The expected number of cases we saw prompted us to take action at this point.”
The CDC’s recommendations shorten isolation periods for infected people from 10 days to five. The agency did not recommend rapid tests before people came out of isolation.
But some scientists argue that rapid tests are the most appropriate indication of whether a person remains contagious or not. Regulatory delays, manufacturing issues and shortages in government support have made rapid testing extremely scarce as the Omicron variant has surged, pushing the number of cases in the United States near record levels.
A scientist who has discussed isolation policies with the CDC in recent months said officials said the agency could not recommend rapid tests because supplies were so scarce. The scientist spoke on condition of anonymity to describe confidential discussions.
President Biden has promised to make 500 million tests available for free, but it’s not clear how soon they will ship.
dr. Walensky denied that the availability of testing affected the agency’s thinking, saying masking only addressed the risk that infected people would remain contagious after isolation. The CDC has asked infected people to wear masks around others for five days after leaving isolation.
“We know that, let’s call it 85 percent, of your portability time is already behind you,” said Dr. Walensky on the five-day isolation period. “A minority of them are right in front of you. And if you wear a mask, you can avert it.”
Scientists said they were concerned that, as with rapid tests, the most effective masks, known as N95s, were out of reach for many Americans.
The Food and Drug Administration said on Tuesday that rapid tests detect Omicron cases, although they may have reduced sensitivity. (Another type of test, known as a PCR, isn’t useful for taking people out of isolation because it can give positive results after someone is no longer contagious.)
A federal official said the CDC included unpublished models about the spread of the Delta variant that showed the risk of transmission was 13 percent five days after someone tested positive. The CDC was working to make that data public, the official said.
However, scientists expressed concern about applying models of Delta’s distribution at a time when Omicron was rapidly becoming dominant. The variant has it considerably easier than Delta infecting vaccinated people. It is also highly contagious, possibly even more so than Delta.
The appropriate isolation periods for Omicron depend on when people test, as well as an individual’s level of immunity and the properties of the variant itself, scientists said. Some people remain contagious for much longer than others, and rapid tests show that certain patients are contagious for more than five days.
“I would be very careful translating data from Delta to Omicron,” said Stephen Goldstein, a virologist at the University of Utah. “I think this could make things worse or speed up the course of the pandemic.”
Immunologists said Tuesday there were also signs that people infected with Omicron were more likely to develop symptoms over the course of infections than with previous variants — a shift that could have major implications for periods of isolation.
Those symptoms, they said, made people more aware of their illness and, in some cases, forced them to get tested earlier. Those people may start the clock on their isolation periods at the very beginning of their infections — rather than the middle or end, as was the case earlier in the pandemic — and go back to work while remaining contagious.
“I don’t think it’s a bad idea to shorten the time for isolation in general,” said Angela Rasmussen, a virologist with the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada. “But saying, ‘Five days is probably OK, based on Delta, so let’s try and see,’ is really not what you should be doing.”
The coronavirus pandemic: important things to know
New CDC Guidelines In hopes of avoiding further disruptions to daily life, the CDC has reduced the period that certain infected Americans must isolate to five days out of 10. This change only applies to those without symptoms, or those without a fever whose other symptoms improve. .
She added: “This could have been implemented in a much more reasonable and less risky way.”
The CDC has long faced criticism for providing confusing guidelines during the pandemic, especially about the use of face masks. Monday’s isolation advice has not allayed those concerns, scientists say.
For example, several doctors said they struggled to understand what patients would fit under the CDC’s advice that infected people whose symptoms “resolved” could leave isolation after five days.
Many people’s symptoms fluctuated over the course of a single day, they said. Other patients may seem to feel better before experiencing a flare-up.
“The counseling is much more confusing than it could and should be,” said Dr. Megan Ranney, an emergency physician and academic dean at Brown University’s School of Public Health.
“Front and center, this should be for people who are not symptomatic. If you have symptoms, you should not be in public.”
dr. Houston Methodist chief executive Marc Boom said he was grateful that the CDC shortened isolation periods for health workers. In the past week, he said, about 3 percent of the workforce had tested positive, putting a greater strain on the hospital than at any other time in the pandemic.
Still, he said the mixed messages were confusing. “They took the public beyond the hospital ground rules,” said Dr. Tree. “That threw us for a loop. We looked at it and said, ‘That makes no sense.’”
Scientists said they expected more data on the course of Omicron infections to emerge in the coming weeks.
Ravindra Gupta, a virologist at the University of Cambridge, said on Tuesday he did not believe that people with Omicron infections would shed the virus longer than people infected with earlier variants, given the signs that it replicated less efficiently in certain human cells.
Infections with earlier variants were found to last about nine days in vaccinated people and 11 days in unvaccinated people, according to studies by NBA personnel, but that didn’t necessarily mean that people were also contagious during that same period.
Denis Nash, an epidemiologist at the City University of New York, said adherence to isolation policies seemed low: A study he led indicated that only 29 percent of people with previous infections had been isolated, although some were unaware they were were sick.
But he said it was not at all clear that shortening the isolation periods would convince more people to stay at home.
“No testing after five days of isolation – is that because the test stock isn’t there?” he said. “If so, that’s no reason to make a policy out of it.”
Noah Weiland reporting contributed.