Officials with the World Health Organization (WHO) last week said fully vaccinated people should continue wearing masks and maintaining social distance to combat the rapidly spreading delta coronavirus variant. But CDC Director Rochelle Walensky on Wednesday stood by the agency's current guidelines, saying fully vaccinated Americans are "safe" from coronavirus variants.

Walensky: 'If you are vaccinated, you are safe'

Walensky on Wednesday said that CDC's guidance on masks hasn't changed in light of WHO's announcement, and that fully vaccinated people don't need to wear masks in most circumstances.

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"If you are vaccinated, you are safe from the variants that are circulating here in the United States," she said, a message that was echoed by White House press secretary Jen Psaki on Wednesday.

"If you have been vaccinated, the message we're conveying is you're safe," Psaki said. "Vaccines are effective, and that is something we want to be very clear with the public about."

Studies have shown that two doses of the Covid-19 vaccine developed by Pfizer-BioNTech prevent about 88% of delta variant infections, and studies released by Moderna suggest its vaccine is also highly effective against the variant.

As of now, Johnson & Johnson (J&J) has yet to release data on how effective its vaccine is against the delta variant as studies are ongoing, but Walensky said that generally "people are agreeing that they anticipate that J&J will perform well against the delta variant as it has so far against other variants circulating in the United States."

Further, research shows that most people who contract the coronavirus after being vaccinated experience only mild symptoms.

Walensky added that WHO is handling a worldwide situation in which fewer people are fully vaccinated than in the United States, and as a result, its guidance is more cautious.

"We know that the WHO has to make guidelines and provide information to the world," she said. "Right now, we know as we look across the globe that less than 15% of people around the world have been vaccinated and many people of those have really only received one dose of a two-dose vaccine. There are places around the world that are surging."

Local authorities are reconsidering mask recommendations

Despite CDC's guidance, some local officials are reevaluating their masking guidance for their residents as the delta variant spreads.

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For instance, health officials in Los Angeles County in California on Monday recommended that "everyone, regardless of vaccination status, wear masks indoors in public places as a precautionary measure."

Barbara Ferrer, public health director for the county, said the recommendation was needed because Covid-19 infections have increased and many people in the county remain unvaccinated.

"We don't want to return to lockdown or more disruptive mandates here," Ferrer said. "We want to stay on the path we're on right now, which is keeping community transmission really low."

How should individuals approach mask-wearing?

Public health experts outside of CDC suggested that individuals may want to consider their own personal risk factors when weighing whether to wear a mask.

"At this point, thinking about wearing a mask is a little like dressing for the weather," Linsey Marr, a professor of civil and environmental engineering at Virginia Tech, said. "You need to consider the caseload and vaccination rates wherever you're going, what activity you'll be doing, and your own health."

Marr said her advice to a fully vaccinated friend would be to follow the mask-wearing rules in her community and be especially careful in certain environments.

"I would tell them that, in general, they do not need to wear a mask," Marr said. "But they should continue to carry one with them for times when they are in a very crowded indoor setting for a long period of time, like air travel, where masks are required anyway, or a crowded movie theater, playhouse or concert venue, for example."

Paul Offit, a professor at the University of Pennsylvania and member of FDA's advisory panel, said the risk of a fully vaccinated person developing Covid-19 increases in communities where vaccination rates are low.

"If you're in a highly vaccinated community, you have sort of a moat around you," he said.

Gregg Gonsalves, assistant professor of epidemiology at the Yale School of Public Health, said even though he's fully vaccinated, he's going to keep wearing a mask in the grocery store and in public areas until vaccination rates increase.

"Am I going to wear a mask among friends who are fully vaccinated? Probably not," he said. "However, in public, I certainly will. This is about promoting a social norm: Right now there are enough people unvaccinated that we should be modeling good behavior, showing social solidarity." (Sullivan, The Hill, 6/30; Teague, CNET, 6/30; Parker-Pope, New York Times, 6/30; Weintraub, USA Today, 6/30; Rabin et al., New York Times, 6/29; Nirappil, Washington Post, 6/30; Coleman/Marcos, The Hill, 7/1; Hannon et al., Wall Street Journal, 7/1).