Outdoor activities are safe without masks — regardless of whether a person is vaccinated — as long as people are either alone or with immediate family members, the Centers for Disease Control and Prevention said Tuesday. And fully vaccinated people can gather safely outdoors without masks in small groups.

The new guidance is part of an update from the agency on what activities are safest for Americans, depending on whether they are fully vaccinated; that is, those who are two weeks out from their last dose of Covid-19 vaccine.

People who are fully vaccinated should also feel comfortable without face coverings outside with other small groups when it's unclear whether others have had their shots.

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Fully vaccinated individuals may safely go without a mask when dining at outdoor restaurants with people from multiple other households. The CDC said that activity is less safe for non-vaccinated people, who should remain masked as much as possible when dining outdoors.

But for other activities, the CDC still recommends wearing a mask, even for vaccinated individuals. Those include attending crowded, outdoor events, such as concerts or sporting events, attending full-capacity indoor religious services, and working out in indoor gyms.

Such activities are not considered safe for people who remain unvaccinated, according to the CDC.

This appears to be the CDC's "attempt to provide some reward for people who have been vaccinated, and to help persuade people who still are unvaccinated," said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Nashville, Tennessee.

But Schaffner added the guidance is so dense that it may be not easy for many people to use it. "This is pretty complicated. You almost have to keep these guidelines with you to figure out, 'can I do this, or can I not do this?'"

"I don't see this being a major driver of change in behavior," said Dr. James McDeavitt, senior vice president and dean of clinical affairs at Baylor College of Medicine in Houston. "Frankly, I think what we've seen is that the CDC recommendations have sort of followed what the general public is doing and hasn't led what the general public is doing."

Dr. Nahid Bhadelia, an infectious disease physician and medical director of the special pathogens unit at Boston Medical Center, told MSNBC Tuesday, "It's important for people to understand how much safer outdoors is compared to indoors."

The CDC needs to "continue to show the importance of indoor masking," Bhadelia said. "We really shouldn't be letting our guard down there."

The guidance cannot account for every scenario or situation for every person, which means many people will still have to use common sense when deciding whether to attend outdoor events, and if so, whether they should be wearing a mask.

People with compromised immune systems, for example, should still protect themselves regardless of their vaccination status, Schaffner said.