This story has been updated to include CDC recommendations released April 27.

More than 94 million Americans are fully vaccinated against the coronavirus. Despite so many invigorated immune systems, the populace still needs to keep wearing masks, public health specialists say.

The country is not yet so protected it can forgo face coverings everywhere. Case counts have spiked in some hot spots. Meanwhile, it’s clearer than ever that masks protect wearers as well as those nearby.

“Masks are one of the best interventions that we have to prevent viral transmission from one person to another,” said Lisa Maragakis, an infectious-disease epidemiologist at Johns Hopkins University School of Medicine.

As new variants of the coronavirus spread within the United States, health professionals have suggested that Americans wear two masks. (John Farrell/The Washington Post)

But the newly vaccinated would be forgiven for giving their masks a second look. In the first wave of vaccinations, after the Food and Drug Administration authorized the Pfizer-BioNTech vaccine in December, even front line health-care workers had these kinds of questions.

“I was caught off-guard at the beginning,” Maragakis said. “My own colleagues started saying, ‘I’m vaccinated, let’s roll back all of our policies.’ And it’s been very difficult to hold the line and say, ‘Wait, wait, wait, it’s not time yet.’ ”

What are mask recommendations for people who are vaccinated?

In March, the Centers for Disease Control and Prevention issued guidelines for what fully vaccinated people can do. Some restrictions were loosened: People who are fully immunized can socialize with each other, ignoring masks and physical distancing. It’s also okay to relax those precautions when meeting with non-vaccinated, low-risk members of a single household.

In April, the CDC released additional guidance for when immunized people can be barefaced. Outside, without lots of other people around, fully vaccinated people no longer need to wear masks. Activities such as walking, biking and hiking can be done without masks.

But, indoors and in busy public spaces, where it might be unknown who is vaccinated or is at risk for severe disease, everyone should continue to wear masks, the agency said.

Those guidelines “are absolutely appropriate for this moment in time,” said Megan Ranney, an emergency medicine physician and professor at Brown University. “There just aren’t enough of us who have immunity yet for it to be safe to take those masks off in public.”

The country will get there, she said. There’s no precise percentage at which the nation suddenly becomes virus-proof; achieving herd immunity is not like toggling on a switch. But Ranney suggested that, as the country reaches 70 to 80 percent of adults vaccinated, “then we’re going to be able to operate in public more like we currently do in private.”

There are a few reasons the CDC’s advice depends on the setting. The coronavirus vaccines authorized by the FDA protect people from severe disease and death, although in extremely rare cases people who are vaccinated can still test positive.

“This is not to undermine or discredit the vaccine in any way — because we know they’re highly efficacious at preventing severe disease — but they’re not 100 percent,” Maragakis said.

Likewise, there are encouraging signs that vaccines reduce transmission, but it is not yet definitive that they halt spread completely. “If you’re vaccinated, then you have that protection for your own health,” Maragakis said. “There is still that chance that you could be a vector and put other unvaccinated individuals at risk.”

Masks complement vaccines. There are persuasive observations that face coverings are protective. States with the lowest levels of mask-wearing were more likely to have higher infection rates, according to a recent PLOS One analysis of the 50 states plus D.C., which examined caseloads and masks from late spring 2020 into early fall.

And, if everyone wore them, masks were nearly 80 percent effective at stopping coronavirus transmission within a home in an observational study of Beijing households. The authors of a scientific review in the Proceedings of the National Academy of Sciences, who compiled evidence from the Beijing study and others, arrived at a strong endorsement of “widespread face masks in public.”

You’re vaccinated and headed to an event. Do you need to wear a mask?

Fans are back at ballparks. High schools and colleges are planning in-person graduation ceremonies this spring. States that had banned large gatherings are once again permitting events, such as New York’s 150-person-maximum wedding rule.

When deciding to wear a mask to an event, experts told The Washington Post that people should assess their risk and their tolerance for it. Risk depends on a variety of factors, such as attendance numbers, a venue’s ventilation, vaccination status and whether people may be immunosuppressed or have other susceptibilities to severe disease.

Chances of transmission are generally reduced, and often greatly so, outdoors. Health specialists are most concerned by people clumping together, not brief encounters that might occur in an open-to-the-public space, such as when walking a dog or hiking. Vaccinated people can ditch masks when attending a small outdoor gathering, even if joined by people who aren’t vaccinated, or dining at an outdoor restaurant, according to the CDC’s latest recommendations.

These activities all share common characteristics: They occur outside, and don’t involve crowds.

“What we know is that outdoors is a much lower risk — orders of magnitude lower risk — than gathering indoors,” Maragakis said.

Maragakis would recommend wearing masks and distancing at large open-air gatherings like ballgames, until the rate of vaccination among the general population is higher. Plus, private venues such as stadiums are allowed to have rules requiring mask-wearing. The CDC, too, advises vaccinated people should wear masks at parades, concerts or other large outdoor events.

At a high school graduation, younger students might not have had access to the vaccine, or there could be older adults in attendance at higher risk of getting sick, making masks appropriate. But at a small wedding ceremony where everyone is vaccinated, Ranney said, “it may be okay to be without masks.” She, for instance, is planning to attend a get-together with about 15 other doctors and health care providers — they’re all vaccinated, and later this month, they’ll share a drink for the first time since the pandemic began.

When will we stop wearing masks?

Israel, whose population is among the most highly vaccinated in the world, removed its outdoor mask mandate April 18.

That could be a sign of what’s to come in the United States in the warmer months. “I fully expect and support mask mandates, by and large, being lifted by early summer,” Ranney said, as long as every American who wants a vaccine has had a chance to get one.

But even if that comes to pass, that doesn’t mean masks will vanish. People should still be allowed to wear masks if they desire, Ranney said, especially those who are particularly vulnerable.

And it’s likely mask-wearing will be encouraged, if not enforced, in higher-risk environments. Such candidates include crowded or poorly ventilated areas, at transportation hubs and while aboard buses, trains and planes.

“Certainly, I’m going to wear masks on long-distance flights,” said Jose-Luis Jimenez, an aerosol chemist at the University of Colorado at Boulder who studies how the virus spreads in the air. “The U.S. can be a curious place, sociologically, but I think I won’t be the only one,” he said, suggesting masks on transit could become as ubiquitous as ball caps.

And masks may be needed again during the fall and winter seasons, when respiratory viruses spread more readily. For the past several flu seasons, wearing masks has been the rule for patients, staff and visitors alike at Johns Hopkins’ oncology center, Maragakis pointed out.

What might our mask-wearing future look like?

Some public health researchers believe masks could transition into a commonplace habit, much like placing toddlers in car seats or slathering sunscreen at the beach. After the pandemic, more than half of Americans expect to wear masks at least some of the time, according to a YouGov survey in March. And 1 in 4 people said they predict frequent mask-wearing.

Helene-Mari van der Westhuizen, a physician who is studying infection control at Oxford University, said masks have become a social practice that transcends their medical purpose, as she wrote with colleagues in the British Medical Journal. She said mask guidance that treats the public by “pretending that we are all in a giant medical ward” misses something: People want masks that are meaningful or accessible.

“That might mean the mask needs to have a nice pattern and fit with the outfit,” she said. (See: the matching masks at last month’s Grammy Awards.) “It should mean that they’re able to pop it in the laundry with their clothing.” To those who wear them, masks can be visual symbols of solidarity against the shared threat of the pandemic — particularly valuable at a time when distancing restrictions can hinder a sense of community.

Masks certainly will not be universal. People have violently acted out their anti-mask sentiment, such as a woman caught on video who coughed on an Uber driver and tore off his mask. Van der Westhuizen said she was flooded with abuse on social media after publishing the BMJ article.

“I hope that we normalize mask-wearing a little bit more, like Japan or South Korea or other countries where people can choose to mask — not because they’re forced to — but because they see it as a way to protect their health,” Ranney said.

The public health experts get that everyone is tired of masks. But, Maragakis said, “we would be foolish” to not consider wearing our masks in the future.