Data from several states and other countries show that the variant behaves differently from previous versions of the coronavirus, she added: “This new science is worrisome and unfortunately warrants an update to our recommendation.”
“This is not a decision we at C.D.C. have made lightly,” Dr. Walensky added. “This weighs heavily on me.” Americans are tired and frustrated, she said, and mental health challenges are on the rise.
After the agency’s announcement, White House staff were instructed to begin wearing masks again indoors. The Biden administration is considering requiring all federal employees to be vaccinated or to submit to regular testing and workplace restrictions, requirements similar to those being imposed in New York City and California.
“We have a pandemic because of the unvaccinated, and they’re sowing enormous confusion,” President Biden told reporters on Tuesday. “The more we learn about this virus and the Delta variant, the more we have to be worried and concerned. And there’s only one thing we know for sure — if those other hundred million people got vaccinated, we’d be in a very different world.”
The C.D.C. needed to revisit its recommendations, said Dr. Anthony S. Fauci, the administration’s lead adviser on the pandemic. “I don’t think you can say that this is just flip-flopping back and forth. They’re dealing with new information that the science is providing.”
The vaccines remain remarkably effective against the worst outcomes of infection with any form of the coronavirus, including hospitalization and death. But the new guidelines explicitly apply to both the unvaccinated and vaccinated, a sharp departure from the agency’s position since May that vaccinated people do not need to wear masks in most indoor spaces.
Those recommendations, which had seemed to signal a winding down of the pandemic, were based on earlier data suggesting that vaccinated people rarely become infected and almost never transmit the virus, making masking unnecessary.