The same applies to dining at a restaurant outside, and to small outdoor gatherings that include some unvaccinated people, the U.S. Centers for Disease Control and Prevention said Tuesday.
Yet vaccinated people should still wear masks in public settings indoors and outdoors where there is a substantial risk of Covid-19 transmission, such as concerts, sporting events and other crowded gatherings, the CDC said.
The fully vaccinated should also wear masks at indoor gatherings with unvaccinated people, visits to a barber, hair salon, shopping mall, museum, movie theater or crowded house of worship. Vaccinated people should also wear masks if singing in an indoor chorus, the CDC said.
The new guidelines are the latest easing restrictions for vaccinated people. They follow mounting scientific evidence indicating the risk of infection is low outdoors, especially among people who are vaccinated. The risk of Covid-19 transmission by vaccinated people is low, evidence shows.
Federal health officials said they hope the revisions will help persuade millions of people who are reluctant or otherwise haven’t been inoculated to get the shot amid a recent decline in demand.
“The message is clear: ‘You’re vaccinated, guess what? You get to return to a more normal lifestyle. If you’re not vaccinated, you’re still in danger,” Health and Human Services Secretary Xavier Becerra said Tuesday in an interview with CBS This Morning.
Paul Sax, clinical director of the infectious diseases division at Brigham & Women’s Hospital in Boston, applauded the changes because they were based on the science of Covid-19 transmission. “It will motivate people to get vaccinated,” he said. “They’re using a carrot rather than a stick.”
The CDC, the federal government’s public-health agency, sets the voluntary guidelines to steer local leaders. The agency has been setting and reworking guidelines throughout the pandemic, as its dynamics have changed and researchers developed better understanding of the virus.
Many public-health authorities have for months encouraged masking as a key tool for reducing the risk of infection and transmission, though it has emerged as a political issue in some states.
The CDC didn’t previously recommend masks be worn outdoors for all activities. The agency had said on its website that “masks may not be necessary when you are outside by yourself away from others, or with people who live in your household.” Some places, however, require people to wear masks when out in public.
Existing CDC guidance said that fully vaccinated people could gather privately in small groups without masks or physical distancing, and travel without putting themselves at serious risk or needing to quarantine as long as they wear masks and take other precautions.
With the new guidelines, federal officials are trying to help vaccinated people resume some aspects of a normal life while preventing further transmission of Covid-19.
Vaccination appears to help slow spread of the virus, health experts said. To relax pandemic restrictions, health authorities have been racing to inoculate more people as a more transmissible variant has taken hold in parts of the U.S.
More than a year of research and outbreak investigations have shown that the risk of catching the virus drops considerably outdoors. The research indicates the risk is higher indoors, where the tiny air particles carrying the virus are more likely to linger and circulate, especially in crowded places with poor ventilation.
“The data are overwhelming that the real risk is indoors,” said John Brooks, chief medical officer for the CDC’s Covid-19 response.
Transmission outdoors isn’t impossible, according to researchers, especially in more crowded conditions or where people may be breathing heavily while in proximity to others.
In a systematic review of outdoor transmission published in November in the Journal of Infectious Diseases, researchers concluded that five Covid-19 studies found that less than 10% of reported transmission reported in outdoor settings. The studies also showed that the odds of super-spreading are much lower outdoors.
“We have unlimited dilution and unlimited ventilation” outdoors, said Joseph Allen, director of the Healthy Buildings Program and an associate professor at the Harvard T.H. Chan School of Public Health. “We know that the biggest single risk factor for this virus is time indoors.”
Mr. Biden is expected to address the new guidelines in a speech from the White House Tuesday.
Upon taking office in January, Mr. Biden had asked the American public to wear a mask for the first 100 days of his presidency. He also signed an executive order requiring that masks be worn on federal property and in airports and certain public transportation.
Mr. Biden’s administration has focused in recent months on accelerating the pace of vaccinations, declaring a ‘wartime’ effort against a pandemic that has claimed more than 572,000 lives and infected more than 32 million in the United States.
The administration has set up federally supported mass vaccination sites across the country, expanded a federal partnership with retail pharmacies and moved up a deadline to make the vaccine available to all eligible Americans by April 15.
The average number of doses administered each day rose steadily and peaked at 3.38 million this month, but it has dropped more recently amid waning demand. According to the Centers for Disease Control and Prevention, more than half of Americans have received at least a first dose of the vaccine.
Still, Mr. Biden has urged Americans to remain vigilant amid concerns over variants rapidly spreading across the country. The president has called on people to wear a mask in public and voiced disapproval of states that have relaxed mask mandates.
—Caitlin McCabe contributed to this article.
Write to Betsy McKay at email@example.com and Sabrina Siddiqui at Sabrina.Siddiqui@wsj.com