The Centers for Disease Control and Prevention loosened Covid-19 guidelines on Thursday, freeing schools and businesses from the onus of requiring unvaccinated people exposed to the virus to quarantine at home.

The changes are a sharp move away from measures such as social distancing requirements and quarantining, which had polarized much of the country, and effectively acknowledge the way many Americans have been navigating the pandemic for some time. The agency’s action comes as children across the country return to school and many offices have reopened.

“We know that Covid-19 is here to stay,” Greta Massetti, a C.D.C. epidemiologist, said at a news briefing on Thursday. “High levels of population immunity due to vaccination and previous infection, and the many tools that we have available to protect people from severe illness and death, have put us in a different place.”

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