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Federal health officials’ decision to shorten isolation times for coronavirus-infected Americans received both fierce support and intense opposition from scientists on Tuesday, particularly due to the lack of a testing requirement and fears that neglect could accelerate the spread of the highly contagious Omicron. variant.

This new guidanceArriving amid the new infections that are starving many hospitals, it seemed to some scientists a necessary step to bolster their workforces in key industries. And encouraging people to come out of isolation early after a negative test can save them the hassle of staying at home for a long time.

But allowing hundreds of thousands of infected people to drop these tests – most importantly, even if their symptoms have not completely cleared – risks creating new cases and putting further pressure on already overburdened health systems, experts said in interviews Tuesday.

“To me it honestly sounds more about economics than about science,” said Yonatan Grad, an associate professor of immunology and infectious diseases at the Harvard TH Chan School of Public Health. Coronavirus infections tracked in the National Basketball Association.

“I suspect it will result in at least some people coming out of isolation faster and therefore there will be more opportunity for transmission and this of course will accelerate the spread of Covid-19,” he added. they were unlikely to adhere strictly to masking recommendations after coming out of isolation.

Director of the Centers for Disease Control and Prevention, Dr. Rochelle P. Walensky said in an interview Tuesday that the new guidance is required by the volume of people about to become infected.

At a series of holiday weekend meetings, he said agency officials had data on transmissibility for past variants and signs that Omicron was causing less severe illness. But ultimately, Dr. Walensky said he decided that the rapid tests were not effective enough in diagnosing contagion in humans.

“You don’t necessarily need to do a test if you don’t know what to do with the result,” he said, adding: “The expected number of cases we’re seeing requires us to act now. ”

This CDC’s recommendations shorten isolation times For infected persons from 10 days to five. The agency did not recommend rapid testing before people come out of isolation.

But some scientists argue that rapid tests are the most appropriate indicator of whether someone is contagious. As the Omicron variant has grown, regulatory delays, production issues, and lack of government support have left rapid testing in extremely poor supply, pushing caseloads to near record levels in the United States.

A scientist who discussed isolation policy with the CDC in recent months said officials said the agency couldn’t recommend rapid tests when supplies were so scarce. The scientist spoke on condition of anonymity to reveal the secret discussions.

President Biden has promised to make 500 million tests available for free, but it’s unclear how quickly these will ship.

Dr. Walensky denied that the testing facility had influenced the agency’s thinking, saying that masking alone addresses the risk of infected people remaining contagious after isolation. The CDC has required infected people to wear masks in front of others for five days after coming out of isolation.

Dr. “We know, let’s say 85 percent, we know your contagion period is already behind us,” Walensky said of the five-day isolation period. “A minority is ahead of you. And if you wear a mask, you can prevent it.”

The scientists said they were concerned that, like rapid tests, the most effective masks known as N95s remained out of reach for many Americans.

The Food and Drug Administration said on Tuesday that rapid tests Detects cases of Omicron, but may have decreased sensitivity. (Another type of test known as PCR isn’t useful for rescuing people from isolation because it can produce positive results when a person is no longer contagious.)

A federal official said the CDC included unpublished modeling on the spread of the Delta variant, which found that five days after someone tested positive, the risk of transmission was 13 percent. The CDC is working to make this data public, he said.

But scientists have expressed concern about applying Delta’s diffusion patterns at a time when Omicron was rapidly becoming dominant. The variant has a much easier time infecting vaccinated people than Delta. It is also highly contagious, potentially even more contagious than Delta.

Correct isolation times for Omicron depend on when people test, as well as an individual’s immunity level and characteristics of the variant, the scientists said. Some people remain contagious for much longer than others, and evidence from rapid testing suggests that some patients are contagious for longer than five days.

“I would be very careful about translating data from Delta to Omicron,” said Stephen Goldstein, a virologist at the University of Utah. “I think this has the potential to make things worse or accelerate the course of the pandemic.”

Immunologists said on Tuesday that there are signs that people infected with Omicron develop symptoms earlier in the course of infection than variants past – a shift that could have major consequences for periods of isolation.

They said these symptoms make people aware of their illness sooner, and in some cases force them to get tested sooner. These people may be starting the clock during their isolation period at the very beginning of their infection and returning to work while remaining contagious, rather than in the middle or end of the pandemic as before.

“I don’t think it’s a bad idea to reduce the isolation period overall,” said Angela Rasmussen, virologist in the Vaccines and Infectious Diseases Organization at the University of Saskatchewan in Canada. “But saying, ‘For Delta, five days is probably fine, so let’s give it a try and see’ isn’t really what you should do.”

“This could have been implemented in a much more reasonable and lower risk way,” he added.

The CDC has long faced criticism during the pandemic, particularly for publishing confusing guidance on the use of face masks. The scientists said Monday’s isolation advice did little to address these concerns.

For example, several doctors said they had trouble grasping what patients would comply with, given the CDC’s recommendation that infected people whose symptoms are “resolving” can come out of isolation after five days.

They said that many people’s symptoms fluctuate over the course of a single day. Other patients may seem to feel better before they have a flare-up.

D., an emergency room physician and academic dean at Brown University’s School of Public Health. “This guide is much more confusing than it should and should have been,” said Megan Ranney.

“Front and centre, this should be for non-symptomatic people. If you have symptoms, you shouldn’t go out in public.”

Houston Methodist’s CEO, Dr. Marc Boom said he’s grateful that the CDC has shortened isolation times for healthcare workers. Last week, he said roughly 3 percent of the workforce had tested positive, pushing the hospital harder than at any other point in the pandemic.

Still, he said the mixed messages are confusing. Dr. “They took the public beyond basic hospital rules,” Boom said. “This threw us into a loop. We looked at it and said, ‘This doesn’t make any sense’.”

The scientists said they expect more data to emerge on the course of Omicron infections in the coming weeks.

Ravindra Gupta, a virologist at the University of Cambridge, said Tuesday that he does not believe people with Omicron infection will spread the virus longer than people infected with previous variants. replicates less efficiently in some human cells.

Infections with previous variants lasted roughly nine days in vaccinated people and 11 days in unvaccinated people, according to research from NBA staff, but that didn’t mean people were contagious during the same period.

Denis Nash, an epidemiologist at the City University of New York, said compliance with any isolation policy seems low: work led by He noted that only 29 percent of people who have been infected in the past are isolated, but this includes those who never knew they were sick.

But he said it was not at all clear that shortening isolation times would persuade more people to stay at home.

“No testing after five days of isolation – is that because there is no testing source?” said. “So there is no reason to make it a policy.”

Noah Weiland contributing reporting.