CDC on Thursday issued new guidance saying that fully vaccinated Americans can forgo masks in most situations both indoors and outdoors—and while some experts praised the guidance as overdue, others worried it was premature.

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Details on the new guidance

In the new guidance, CDC said that Americans who have received their final Covid-19 vaccine dose at least two weeks previously—meaning the second shot of either Pfizer/BioNTech's or Moderna's Covid-19 vaccine, or the single shot required for Johnson & Johnson vaccine—can be without a mask and do not need to socially distance in most settings.

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"Anyone who is fully vaccinated can participate in indoor and outdoor activities, large or small, without wearing a mask or physically distancing," CDC Director Rochelle Walensky said. "If you are fully vaccinated, you can start doing the things that you had stopped doing because of the pandemic. We have all longed for this moment when we can get back to some sense of normalcy."

There are, however, some exceptions. According to CDC, vaccinated Americans should continue wearing masks in health care facilities, such as hospitals; on public transit and during air travel; when around the immunocompromised; and in congregate settings, such as homeless shelters or jails. Vaccinated Americans should also continue to abide by local and federal mask mandates, CDC said.

"The whole country is not a homogeneous space," Walensky said. "So, we have some jurisdictions that have higher levels of cases. We have some jurisdictions that have lower levels of vaccine administration."

Further, CDC said vaccinated Americans don't need to get tested before or after domestic travel unless required by local, state, or territorial health authorities. When traveling internationally, CDC said, vaccinated Americans should still get tested within three days before their flight and within three to five days after their trip.

Meanwhile, unvaccinated Americans should continue wearing masks and social distancing, CDC said. "If you are not fully vaccinated, you are not fully protected and so you need to be continuing to wear your mask and practicing all of the mitigation strategies that we've been discussing before," Walensky said.

Walensky said the new recommendations come as a result of a significant drop in Covid-19 cases nationwide, an increase in vaccine availability, and a "coalescence" of research showing how effective the vaccines are against variants of the new coronavirus and at preventing viral transmission.

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CDC added that it could change its guidance if Covid-19 case numbers spike again.

President Joe Biden said the new guidance is "a great milestone, a great day" that has "been made possible by the extraordinary success we've had in vaccinating so many Americans so quickly."

"We've gotten this far. Please protect yourself until you get to the finish line," Biden said. "Get vaccinated or wear a mask until you do."

Experts react with a mix of praise and hesitation

Some public health experts praised the guidance, saying it reflects the most recent research on vaccines' effectiveness.

"I'm ecstatic about this news! It's evidence-based and it's bold," Uché Blackstock, CEO of Advancing Health Equity, said. "I hope that the updated guidelines incentivize more people to get vaccinated."

However, Leana Wen, former health commissioner for Baltimore, said she was "shocked" by the new guidance. "We have gone from one extreme to the other," she said.

Wen said she had hoped mask recommendations would be lifted in areas that have reached vaccination rates of 70%. "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?"

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Shereef Elnahal, former New Jersey state health commissioner and CEO of University Hospital in Newark, said, "You're still dealing with a situation where an overwhelming majority of the community is not fully vaccinated. 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."

Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, acknowledged that, "[g]iven vaccination rates in some places, there's the possibility that things might go awry locally," but added that "the benefit in terms of encouraging people to get the shot among those who don't like their masks might well outweigh it."

John Moore, a virologist at Weill Cornell Medicine, said individuals will have to assess their own comfort and risk in certain situation, depending on how large a gathering is and the number of Covid-19 cases in the community.

"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."

Moore's perspective was broadly reflected in a New York Times poll of 723 epidemiologists that was conducted before the new CDC guidance was released. Just 5% of respondents to the poll said vaccinated people should wear masks while outdoors and mostly alone, such as when exercising, but 25% said vaccinated people should wear masks when within six feet of others, and 88% said vaccinated people should do so when in a large crowd.

Several poll respondents told the Times that they were motivated to continue mask-wearing largely out of a desire to protect others, rather than themselves.

"While I am comfortable taking personal risks, I would not tolerate risks that could harm others," Kevin Andresen, who leads the Covid response team at the Colorado Department of Public Health, told the Times. "Covid precautions protect everyone, not just me" (Banco/Lim, Politico, 5/13; Cohen, Roll Call, 5/13; Wingrove/Court, Bloomberg/Washington Post, 5/14; Leonhardt, New York Times, 5/14; Rabin et. al., New York Times, 5/13; Lopez, Vox, 5/13; Wamsley, NPR, 5/13 [1]; Wamsley, NPR, 5/13 [2]; Romo, NPR, 5/13; Lopez, Vox, 5/11; Sanger-Katz, "The Upshot," New York Times, 5/12).