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Should fully vaccinated people continue to wear masks? Experts weigh in.

"Do whatever it takes for Covid to go away," one doctor said. That includes continuing to wear a mask.

More than 156 million people in the U.S. have been fully vaccinated. But even though the Covid-19 vaccines are very effective against all the known coronavirus variants, including the highly transmissible delta variant that is spreading rapidly, some communities and physicians are urging a return to masking.

On Thursday, the St. Louis County and city public health departments issued a warning about the spread of the delta variant and advised a return to masks indoors, even if vaccinated. Earlier in the week, the Los Angeles County Department of Public Health announced it "strongly recommends" that everyone wear a mask indoors after an increase in cases.

People wait to cross the street in downtown Chicago on May 22, 2021.Nam Y. Huh / AP file

But despite a slowdown in the rate of vaccinations and the recent uptick in Covid-19 cases in the U.S., there is no indication the Centers for Disease Control and Prevention will once again recommend masks for fully vaccinated individuals for the country as a whole.

"If you're vaccinated, you have a very high degree of protection from all of the variants that we are aware of circulating in the United States," Dr. Rochelle Walensky, director of the CDC, told NBC News.

When would masks be needed?

In areas with low vaccine uptake, a return to masks indoors, even for vaccinated people, may be appropriate, Walensky said. Nationwide, just over 55 percent of Americans eligible for the Covid-19 vaccine have been fully vaccinated.

Do whatever it takes for Covid to go away.

"If you're in a community that has a high amount of disease and less than a third of your population is vaccinated, one should consider whether the policy should be to mask," Walensky said. Masking is "more about protecting the two-thirds of the community that are not vaccinated."

Currently, approximately 1,000 counties in the U.S. have vaccination coverage of less than 30 percent, she said.

Full coverage of the coronavirus outbreak

In Wyoming, for example, just over 31 percent of the population is fully vaccinated, according to the state's Department of Health. That means the vast majority of residents — 69 percent — remain susceptible to Covid-19. That's why Dr. Andy Dunn, a family physician and chief of staff at Wyoming Medical Center in Casper, wants vaccinated people to continue with masking.

"These variants are going to find a way" to survive, Dunn said.

"Do whatever it takes for Covid to go away," he added. "If I had to jump on my left foot five times a day, I would do it."

Can you get Covid-19 if you're fully vaccinated?

No vaccine stops all transmission of a virus. While rare, it is possible that fully vaccinated people can become infected with Covid-19. A recent outbreak of Covid-19 cases associated with the delta variant in Israel included many who had been fully vaccinated, for example.

Those are called breakthrough infections, and they are typically mild.

Can fully vaccinated people spread Covid-19 to others?

Science's best guess right now is "maybe."

"There is no study that looks at vaccinated people and their asymptomatic carry rate with the delta variant," said Dr. Hugh Cassiere, director of critical care services at the Sandra Atlas Bass Heart Hospital at North Shore University Hospital, on Long Island, New York.

"That's the scary part," Cassiere said. "Delta has such a high infectivity rate."

While vaccinated individuals may be protected personally, a mask protects people who are vulnerable, including those who are unvaccinated, people with compromised immune systems and children under age 12.

"A mask reduces your infectivity to me, and mine to you. It's bi-directional," said Cameron Wolfe, an infectious diseases expert and an associate professor of medicine at Duke University School of Medicine.

Masks were considered highly effective in slowing the spread of the virus last fall, but that was before widespread access to vaccines.

Still, "if we're dealing with something that is more transmissible," Wolfe said, referring to the delta variant, "I think you'd want a little more protection."

Experts say perhaps it is time to re-normalize mask-wearing for the benefit of all.

"The critical people to have masks are the unvaccinated," said Dr. Marybeth Sexton, an assistant professor of infectious diseases at Emory University School of Medicine. "But sometimes I think it's probably necessary for everybody to mask in order to accomplish that."

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Some doctors treating severe Covid-19 cases are also encouraging universal mask use not necessarily for less risky outdoor gatherings, such as Fourth of July barbecues and pool parties, but for more crowded, indoor areas, where patrons probably don't know with whom they're sharing a space, such as a movie theater.

Those are "higher-risk situations," said Dr. Russell Vinik, chief medical operations officer at the University of Utah Health in Salt Lake City. "With so many unknowns now, it is prudent to wear a mask. I certainly do."

There is also no indication that wearing a mask causes physical harm.

"We've been doing it for 12 months pretty solidly," Wolfe said. "It's not that hard."

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