The Centers for Disease Control and Prevention announced a shorter suggested quarantine period for some health care workers whove tested positive for COVID-19 , saying Thursday that employees who are asymptomatic should be able to return to work after seven days of isolation, shortened from 10, and a negative coronavirus test.

The new guidelines also state that isolation time can be cut further if there are staffing shortages and that health care workers whove received all vaccine doses, including a booster, do not need to quarantine after a high-risk exposure.

As the healthcare community prepares for an anticipated surge in patients due to Omicron, CDC is updating our recommendations to reflect what we know about infection and exposure in the context of vaccination and booster doses, Dr. Rochelle Walensky, the CDC director, said in a statement .

Our priority remains prevention, she added, and I strongly encourage all healthcare personnel to get vaccinated and boosted.

The decision comes as scientists piece together new information about the omicron variant of COVID-19, which is now the dominant strain in the U.S. This week, three separate research teams around the world released findings that omicron infections result in mild illness more often than with previous strains. Studies have also shown that the third doses of the Pfizer-BioNTech and Moderna vaccines may offer significant protection against the omicron variant.

But just 62% of Americans are fully vaccinated and even less have gotten the booster shot, so hospitals anticipate needing as many workers as possible to handle an influx of new cases, especially following widespread holiday travel and family gatherings, experts have warned.

At least one group representing health care workers has come out against the new CDC policy. National Nurses United, one of the countrys largest organization of registered nurses, issued a statement saying the guidelines were in effect guaranteeing more transmission in hospitals.

Weakening Covid-19 guidance now, in the face of what could be the most devastating Covid-19 surge yet, will only result in further transmission, illness, and death, the groups president, Zenei Triunfo-Cortez, said in a statement.

The CDC also recently endorsed test-to-stay policies for schools, letting students whove been exposed to the virus remain in classrooms if they test negative. Research into such policies in the Chicago and Los Angeles areas found viral infections did not increase when using that approach.