Will shortened isolation periods spread the coronavirus?

NEW YORK (NYTIMES) - The decision by US federal health officials to shorten isolation periods for Americans infected with the coronavirus drew both tempered support and intense opposition from scientists on Tuesday (Dec 28), particularly over the absence of a testing requirement and fears that the omission could hasten the spread of the highly contagious Omicron variant.

The new guidance, coming amid a crush of new infections that has starved many hospitals of workers, seemed to some scientists like a necessary step to shore up workforces in essential industries.

And encouraging people to leave isolation early after testing negative could spare them the hardships of prolonged periods at home.

But letting hundreds of thousands of infected people forgo those tests - even if, crucially, their symptoms were not entirely gone - risks seeding new cases and heaping even more pressure on already overburdened health systems, experts said on Tuesday.

"To me, this feels honestly more about economics than about the science," said Dr Yonatan Grad, an associate professor of immunology and infectious diseases at the 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 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," he added, noting that people were unlikely to adhere strictly to masking advice after leaving isolation.

Dr Rochelle Walensky, director of the Centres for Disease Control and Prevention (CDC), said on Tuesday that the new guidance had been necessitated by the volume of people about to be infected.

In a series of holiday weekend meetings, she said, agency officials pored over transmissibility data for past variants and signs that Omicron caused less severe illness. But ultimately, Dr Walensky said, she decided that rapid tests were not effective enough at diagnosing infectiousness in people.

"You don't necessarily do a test if you don't know what you're going to do with the result," she said, adding, "The anticipated number of cases that we were seeing required us to take action at this moment."

The CDC's recommendations cut isolation periods for infected people from 10 days to five. The agency did not recommend rapid testing before people left isolation.

But some scientists maintain that rapid tests are the most convenient indication of whether or not someone remains contagious. Regulatory delays, manufacturing problems and shortfalls in government support have left rapid tests in extremely short supply as the Omicron variant surged, pushing caseloads to near record levels in the United States.

According to a scientist who has discussed isolation policy with the CDC in recent months, officials said the agency could not recommend rapid tests while supplies were so scarce. The scientist spoke on condition of anonymity to describe confidential discussions.

President Joe Biden has promised to make 500 million tests available free of charge, but it is not clear how quickly they will be shipped.

Dr Walensky denied that testing availability affected the agency's thinking and said that masking alone addressed the risk that infected people remained contagious after isolation. The CDC has asked infected people to wear a mask around others for five days after leaving isolation.

"We know that, let's call it 85 per cent of your transmissibility time is already behind you," Dr Walensky said of the five-day isolation period. "A minority of it is in front of you. And if you wear a mask, you can avert it."

Scientists said they worried that like rapid tests, the most effective masks, known as N95s, remained out of reach for many Americans.

One federal official said the CDC incorporated unpublished modelling on the spread of the Delta variant that found the risk of transmission was 13 per cent five days after someone tested positive. The CDC was working to make that data public, the official said.

Scientists, though, expressed concern about applying models of Delta's spread at a time when Omicron is fast becoming dominant. The variant has a considerably easier time than Delta infecting vaccinated people. It is also highly contagious, potentially even more so than Delta.

The right isolation periods for Omicron depend on when people are testing, as well as an individual's level of immunity and the properties of the variant itself, scientists said. Some people remain contagious much longer than others, and evidence from rapid tests suggests certain patients are still infectious for longer than five days.

"I'd be very wary of translating data from Delta to Omicron," said Dr Stephen Goldstein, a virus expert at the University of Utah. "I think there's the potential for this to make things even worse or accelerate the course of the pandemic."

Immunologists said on Tuesday that there were also signs that people infected with Omicron were developing symptoms earlier in the course of infection than they did with past variants - a shift that could have major ramifications for isolation periods.

Those symptoms, they said, were making people aware of their illnesses sooner and, in some cases, compelling them to get tested sooner. Those people may be starting the clock on their isolation periods at the very beginning of their infection - rather than at the middle or end, as was true earlier in the pandemic - and returning to work while they remain contagious.

"I don't think reducing the time for isolation overall is a bad idea," said Dr Angela Rasmussen, a virus expert at the Vaccine and Infectious Disease Organisation at the University of Saskatchewan in Canada. "But saying, 'Five days is probably OK, based on Delta, so let's give it a shot and see,' is really not what you should be doing."

She added, "This could've been implemented in a much more reasonable and lower-risk way."