Americans who are fully vaccinated can go without masks or physical distancing in most cases, even when they are indoors or in large groups, federal officials said Thursday, paving the way for a full reopening of society.

The change represents a huge shift symbolically and practically for pandemic-weary Americans, millions of whom have lived with the restrictions for more than a year. A growing number have complained they cannot do more even after being fully vaccinated and criticized the Centers for Disease Control and Prevention for being overly cautious. More than 154 million Americans have had at least one shot and 117 million are fully vaccinated, about 35% of the population.

Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention Susan Walsh/Associated Press

“We have all longed for this moment when we can get back to some sense of normalcy,” CDC Director Rochelle Walensky said at a briefing. “Based on the continuing downward trajectory of cases, the scientific data on the performance of our vaccines and our understanding of how the virus spreads, that moment has come for those who are fully vaccinated.”

Walensky cited a growing body of real-world evidence demonstrating the efficacy of the coronavirus vaccines and noted the shots offer protection even against more contagious variants circulating in the United States. She also noted the rarity of breakthrough infections in those who are fully vaccinated and the lesser severity of the relatively few infections that have occurred.

She did leave open the possibility that the restrictions could return should the pandemic worsen. “This past year has shown us that this virus can be unpredictable,” she said.

The relaxation of masking does not apply to airplanes, buses, trains and other public transportation, to health-care settings, or where state or local restrictions still require them, Walensky said. Officials also noted that some business settings may require masks, especially since some workers may remain unvaccinated.

The CDC director urged those who are immune-compromised to speak with their doctors before giving up their masks, and said that those who are not vaccinated remain at risk for mild or severe illness and death and should still wear masks.

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“The science is . . . very clear about unvaccinated people,” she said. “You remain at risk of mild or severe illness or death or spreading the disease to others. You should still mask and you should get vaccinated right away.”

The updated guidance, which drew criticism from some business and labor groups, means that millions of fully vaccinated Americans can begin returning to pre-pandemic activities, including in-person school and work, which many have eschewed since March 2020. Individuals are considered fully vaccinated two weeks after the one-dose Johnson & Johnson shot, or two weeks after the second dose of either the Pfizer-BioNTech or Moderna vaccines.

In part as a result of accelerating vaccinations, the country is seeing the lowest number of new daily cases it has had in eight months, and deaths have decreased from a high of about 3,000 per day on average in January to about 600 per day, as many of the most vulnerable, including the elderly, have been inoculated.

“This is a day that I think will be marked as a true turning point in the pandemic in the United States,” said Richard Besser, former acting director of the CDC and president and chief executive of the Robert Wood Johnson Foundation. “The idea that people who are fully vaccinated can take off their masks, can go outside, can go inside, be around people and not have to worry about covid anymore, that’s absolutely huge.”

Appearing maskless in the White House Rose Garden Thursday afternoon, President Joe Biden celebrated the update as “a great day for America” and said fully vaccinated people can shake hands and hug again without fear of contracting covid-19. Biden had been criticized for wearing a mask during his recent speech to Congress.

The president, who has set a goal that 70% of American adults be vaccinated by July Fourth, also praised those who had received the shots. “When your country asked you to get vaccinated, you did,” he said. “The American people stepped up. You did what I consider to be your patriotic duty. That’s how we have gotten to this day.”

Still, the guidelines left many questions, especially for businesses struggling with how to protect employees when they return to the workplace, essential workers who have frequent contact with the public and the parents of children younger than 12, who are still ineligible for the shots.

One leading business group said the updated guidance underscores the uncertainty faced by companies trying to decide precautions in the absence of a uniform standard.

Harold Kim, president of the U.S. Chamber Institute for Legal Reform. said commercial establishments have faced an evolving set of federal, state and local guidelines throughout the pandemic – sometimes at odds with one another. “We never had a playbook,” he said.

A union representing 1.3 million grocery and retail workers criticized the guidance as confusing and said it failed to consider the impact on essential workers who face frequent exposure to individuals who are not vaccinated and refuse to wear masks.

“Millions of Americans are doing the right thing and getting vaccinated, but essential workers are still forced to play mask police for shoppers who are unvaccinated and refuse to follow local COVID safety measures,” said Marc Perrone, president of the United Food and Commercial Workers. “Are they now supposed to become the vaccination police?”

A public health law expert said the CDC “has now lurched from overcaution to abandoning caution.”

“It’s clear that outdoor activity is safe without masks and distancing, but indoor venues still pose risks,” said Lawrence Gostin, faculty director of the O’Neill Institute for National and Global Health Law and Georgetown University Law Center. “The difference between a supermarket, a restaurant or a gym (where masks aren’t required) and an airport (where they are) doesn’t make sense and isn’t supported by science.”

The new CDC guidance is likely to be echoed by state and local governments, which typically follow the lead of federal health officials, said Michael Fraser, chief executive of the Association of State and Territorial Health Officials, which represents public health agencies.

Fraser called the policy “a sensible approach, knowing what we know today, which is different from what we knew two months ago or six months ago.”

Federal, state and local officials have worked to counter vaccine indifference or hesitancy by sending out mobile clinics to rural and other hard-to-reach areas and administering vaccinations at sports games and offering incentives such as free tickets, beer, and hunting licenses for those who get a shot.

Ohio’s Republican governor, Mike DeWine, upped the ante Wednesday by saying that five state residents who are vaccinated could win $1 million in a vaccination lottery; he announced a separate drawing for vaccinated teenagers who will be eligible for a full four-year scholarship to state universities.

The Biden administration is also working to boost vaccine education to persuade those who are hesitant to get the shots.

“There’s still work to be done to help people who are questioning, or (who) don’t trust the vaccines. And I’m hoping some of this attention to the ability to do more will motivate some,” said Julie Morita, executive vice president of the Robert Wood Johnson Foundation and a member of Biden’s transition COVID-19 task force.

Sen. Susan Collins, R-Maine, who had grilled Walensky about what Collins had described as overly restrictive guidance at a hearing earlier this week, praised the mask update, but said it was overdue.

“It’s so important that people be able to have confidence in CDC’s guidelines because otherwise they won’t follow them,” Collins said, adding the agency had “lagged the science and the overwhelming opinion of public health experts” on wearing masks outside and on its recommendations for summer camps.

In its summer camp guidance, the CDC has said that masks should be worn by vaccinated adults and children at all times, including outdoors, except when swimming and eating.

Collins, who acknowledged that Maine is a major location for summer camps, called on the agency to update that as well. She noted that children 12 years old and over can now be vaccinated, and that even though younger children can’t get the shots, almost all camp activities are outdoors.

Children under 12 years old who are unvaccinated still need to take precautions, including wearing a well-fitted mask, and the agency is looking to update its guidance for camps soon, said CDC spokesman Jason McDonald.

Others shared Collins’ view that the update was overdue but lauded that it was done.

“This is an important recognition that the level of COVID risk for most people has fallen substantially,” said Scott Gottlieb, an FDA commissioner under President Donald Trump. “We’re well served by CDC’s move today to relax their guidance and give a green light to those who felt bound by their mandates.”

Carlos del Rio, professor of medicine at Emory University in Atlanta, said he believed the update would persuade more people to get the shots.

“Young people say, ‘Why should I get vaccinated? I’m not going to die of this.’ What they want to hear is, ‘You can take your mask off,'” del Rio said, adding that it doesn’t help to promote vaccinations if officials tell people to “get vaccinated, but do the same thing.”

Others defended the CDC, saying it had to move cautiously with a new and unpredictable virus, and arguing that updated guidance was appropriate only after there was sufficient evidence the vaccines were as effective in the real world as they had been in clinical trials.

“To expect the CDC to be nimble and make decisions before it gets the data it needs would be a big mistake,” Fraser said.

Jason Schwartz, an assistant professor of health policy and management at the Yale School of Public Health, acknowledged mixed messages from the CDC but said that reflected “earlier stages of the pandemic and earlier stages of our knowledge about how the virus (is) transmitted.”

The Washington Post’s Isaac Stanley-Becker and William Wan contributed to this story.