Federal health officials on Thursday advised Americans who are fully vaccinated against the coronavirus that they could stop wearing masks or maintaining social distance in most settings, the clearest sign yet that the pandemic might be nearing an end in the United States.
The new recommendations caught state officials and businesses by surprise and raised a host of difficult questions about how the guidelines would be carried out. But the advice came as welcome news to many Americans who were weary of restrictions and traumatized by the past year.
“We have all longed for this moment,” Dr. Rochelle P. Walensky, the director of the Centers for Disease Control and Prevention, said at a White House news conference on Thursday. “If you are fully vaccinated, you can start doing the things that you had stopped doing because of the pandemic.”
Masks had come to symbolize a bitter partisan divide. Setting them aside in restaurants and sidewalks, in museums and shops, would represent not just the beginning of the end of the pandemic but hope for a return to normalcy.
Permission to stop using masks also offers an incentive to the many millions who are still holding out on vaccination. As of Wednesday, about 155 million people had received at least one dose of a Covid-19 vaccine, but only about one-third of the nation, 119 million people, had been fully vaccinated.
And the pace of vaccination has slowed: Providers are administering about 2.09 million doses per day on average, about a 38 percent decrease from the peak of 3.38 million reported in mid-April.
At the White House on Thursday, President Biden hailed the new recommendations as a “milestone” in the nation’s effort to beat back the pandemic and urged Americans to roll up their sleeves for vaccinations.
Still, Mr. Biden urged Americans not to turn on those who were not yet vaccinated. “Please treat them with kindness and respect,” he said. “We’ve had too much conflict, too much bitterness, too much anger, too much politicization of this issue about wearing masks.”
While there may well be scientific justification for the guidelines, they raised a host of questions for which there are no easy answers: How to trust that unvaccinated neighbors will wear masks when they should? What about younger children, for whom no vaccinations have been authorized, and schools? Is it possible to enforce such guidelines?
The new advice arrived just two days after Senate Republicans tore into the C.D.C. for what they called outdated and overly conservative guidance on mask-wearing, accusing the agency at a hearing on the government’s pandemic response of losing the trust of Americans looking to return to normal life.
“Free at last,” a maskless Senator Mitch McConnell of Kentucky, the Republican leader in the Senate, said as he left the Capitol on Thursday.
The agency said that vaccinated Americans would have to continue to abide by existing state, local or tribal laws and regulations and follow local rules for businesses and workplaces. But many local officials and business operators will be hard-pressed to maintain mask requirements now that the federal agency has spoken.
“While we all share the desire to return to a mask-free normal, today’s C.D.C. guidance is confusing and fails to consider how it will impact essential workers who face frequent exposure to individuals who are not vaccinated and refuse to wear masks,” said Marc Perrone, the president of the United Food and Commercial Workers union.
About two dozen states currently mandate masking in public. Connecticut, Pennsylvania and Washington State promptly lifted mask mandates on Thursday after the C.D.C.’s announcement. Governors in states like New York and New Jersey said they would study the C.D.C. recommendations before making any moves.
In some ways, the C.D.C.’s mask guidance has now come full circle. In the early days of the pandemic, health experts expressed ambivalence about whether masks were useful outside hospital settings. It was only in April 2020 that C.D.C. officials determined that masks could slow the spread of the virus and urged Americans to wear cloth masks they could make at home.
President Trump famously resisted wearing a mask, and many of his ardent supporters followed suit. Still, masking became ubiquitous in many parts of the country, and federal health officials have been relentless in advocating their use.
Dr. Walensky said on Thursday that the new recommendations had resulted from a steep drop in coronavirus cases — infections have declined by about a third in the last two weeks — and an increase in the availability of vaccines. She also cited a “coalescence” of new research that showed the vaccine’s effectiveness against virus variants and in preventing transmission.
Some scientists, even those who approved, were startled that an agency renowned for its caution had executed such a swift about-face. Just two and a half weeks ago, the C.D.C. advised fully vaccinated people that they could remove their masks outdoors but not in crowded spaces.
“If you’re healthy and vaccinated, and don’t have any household members who are vulnerable — and if you’re willing to accept risk of mild illness — then it seems like it’s time,” said Linsey Marr, an expert on aerosols at Virginia Tech and a vigorous critic of the agency’s past advice on transmission of the virus.
Still, she warned, “In places where the numbers are still high, it’s riskier even if you are vaccinated.”
Other researchers were unconvinced by the agency’s reasoning. “I am shocked,” said Dr. Leana Wen, former health commissioner for the city of Baltimore. “We have gone from one extreme to the other.”
Dr. Wen said she was hoping that mask recommendations would be lifted locally in regions that had achieved vaccination rates of 70 percent. “We now have a free-for-all,” she said. “No one is checking who is fully vaccinated. What is to stop people from doing whatever they want to do and making everyone else unsafe?’’
Some health leaders in underserved communities also expressed concern that restrictions were being lifted too soon. “You’re still dealing with a situation where an overwhelming majority of the community is not fully vaccinated,” said Dr. Shereef Elnahal, a former New Jersey state health commissioner and chief executive of University Hospital in Newark.
“To lift restrictions without vaccine verification in those areas, which are predominantly minority communities that have had a tough time with the pandemic, would be high risk,” he said.
The C.D.C.’s new advice was sprinkled with caveats. Even vaccinated individuals must cover their faces and physically distance when going to doctors, hospitals or long-term-care facilities like nursing homes and homeless shelters; when traveling by bus, plane, train or other modes of public transportation or while in transportation hubs like airports and bus stations; and when in prisons and jails.
The agency was not specific about masking in some settings, including schools. Dr. Walensky said that agency recommendations would be refined in the coming weeks.
The new federal advice is likely to galvanize Americans who have grown unaccustomed to appearing in public unmasked — or to seeing others do so. “We’ve got to liberalize the restrictions so people can feel like they’re getting back to some normalcy,” Dr. Anthony S. Fauci, the Biden administration’s senior adviser on the pandemic, said in an interview.
But the move could raise alarms among more cautious Americans, who may be reluctant to engage in public activities when more people are unmasked. There is no way to know who is vaccinated and who is not, and the majority of the population is not yet fully vaccinated.
John Moore, a virologist at Weill Cornell Medicine in New York, said people would need to assess their own comfort in different situations, depending on the size of the gathering and the number of cases in the area.
“Would I go to a modest dinner party with vaccinated friends?” he said. “Absolutely. But walking into a bar in a poorly vaccinated state, or walking into a large gathering of people — I would be uncomfortable doing that without a mask.”
“I know people who are of my age who are very very skittish about any form of mingling,” added Dr. Moore, who said he is in his 60s. “It’s going to take a lot of adjustment, but I think it’s a good idea, and appropriate on the science.”
In a sense, the agency is asking that neighbors, colleagues and complete strangers trust one another to do the right thing, some scientists noted. Shedding masks may rekindle a national debate on vaccine passports, as verification of immunity becomes more important in unmasked settings like offices and restaurants.
Ellie Murray, an epidemiologist at the Boston University School of Public Health, said, “Basically, what that relies on, then, is individuals policing people around them, or business owners checking vaccination status in some way or just relying on some sort of honor code.”
In justifying the recommendations, agency officials pointed to several recent studies showing that vaccines are more than 90 percent effective at preventing mild and severe disease, hospitalizations and deaths from Covid-19 in real world settings.
Among them was a study of 6,710 health care workers in Israel, including 5,517 fully vaccinated workers, that found that the Pfizer-BioNTech vaccine was 97 percent effective at preventing symptomatic infections among the fully vaccinated and 86 percent effective at preventing asymptomatic infections among them.
“Vaccinated people are much less likely to transmit than we were worried they might be before, and they are protected themselves,” said Angela Rasmussen, a virologist at the Vaccine and Infectious Diseases Organization in Saskatchewan, Canada. Vaccines in use have proven effective against preventing serious illness and death from known variants of the coronavirus, she added.
Some critics have said the agency’s caution may be undermining faith in the vaccines. The new guidelines may help restore confidence, said Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.
“Given vaccination rates in some places, there’s the possibility that things might go awry locally,” he said, referring to possible outbreaks. But “the benefit in terms of encouraging people to get the shot among those who don’t like their masks might well outweigh it.”
The new guidelines contrasted with rising concerns about indoor air quality. On Thursday, a group of scientific experts called on policymakers and building engineers to prioritize clean air in public buildings to minimize the risk of respiratory infections.
Reduced masking “makes it even more important that workplaces and other buildings ensure that they have good ventilation,” Dr. Marr, a member of the group, said.
It’s unclear whether the C.D.C. plans to modify its recommendations for children. The agency had said that children must wear masks even outdoors while at summer camps, a measure critics have derided as unnecessary.
“I think no matter what, people are always going to be unhappy with the C.D.C.’s recommendations,” Dr. Rasmussen said. “It is always going to be criticized for being either too conservative or not conservative enough.”
Reporting was contributed by Remy Tumin, Adeel Hassan, Nicholas Fandos and Michael Corkery.