Mask-wearing on planes may be here to stay, top federal infectious-disease expert Anthony S. Fauci says.

In an interview on ABC News’s “This Week” on Sunday, he was asked if he believes there will be a point when it won’t be necessary to wear masks during air travel.

“I don’t think so,” he said. “I think when you’re dealing with a closed space, even though the filtration is good, that you want to go that extra step.”

Fauci’s mask-wearing suggestion came as top government health officials sounded the alarm about the rapidly spreading omicron variant, noting that it already accounts for 50 percent of coronavirus cases in parts of the United States. Just as many prepare to travel for end-of-year holidays, health officials warned of a tough winter ahead — strengthening calls for the unvaccinated to get their shots and the vaccinated to get boosted.

Fauci’s comments also follow remarks from Southwest Airlines CEO Gary Kelly, who said during a Senate hearing last week that masks “don’t add much, if anything, in the air cabin environment.”

Kelly, who tested positive for the coronavirus days after the hearing, added: “It’s very safe, very high-quality, compared to any other indoor setting.”

During the same hearing, American Airlines CEO Doug Parker argued an “aircraft is the safest place you can be. It’s true of all of our aircraft — they all have the same HEPA filters and air flow.”

Fauci said Sunday that “even though you have a good filtration system, I still believe that masks are a prudent thing to do, and we should be doing it.”

In separate television interviews, Fauci and Francis S. Collins, whose last day as director of the National Institutes of Health was Sunday, stopped short of calling on people to cancel travel plans. They warned of risks associated with traveling, even for the vaccinated, and urged people to do so carefully.

Fauci advised people to be cautious as they travel.

“If you are vaccinated and boosted and are prudent when you travel, when you're in an airport, to be wearing a mask all the time — you have to be wearing a mask on a plane,” he said.

Collins said the virus “is going to be all around us.”

“I’m not going to say you shouldn’t travel, but you should do so very carefully,” he said in an interview on CBS News’s “Face the Nation.” “People are going, ‘I’m so sick of hearing this,’ and I am, too. But the virus is not sick of us, and it is still out there looking for us, and we’ve got to double down on these things if we’re going to get through the next few months.”

Earlier this year, Fauci said people may decide in the long term to wear masks to help curb the spread of viruses during certain seasons.

In a May interview on NBC News’s “Meet the Press,” he referred to the limited flu activity last season because of widespread public health mitigation measures.

“It is conceivable that as we go on, a year or two or more from now, that during certain seasonal periods when you have respiratory-borne viruses like the flu, people might actually elect to wear masks to diminish the likelihood that you’ll spread these respiratory-borne diseases,” he said.

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