• In an interview Monday on MSNBC's "Morning Joe," Dr. Anthony Fauci said a vaccine mandate for domestic air travel is worth considering.
• International travelers must show proof of vaccination and a negative Covid test in order to board a U.S.-bound flight, and also wear a mask.
• Later on Monday, Fauci said he didn't think a mandate would be imposed any time soon.

The federal government should consider requiring Covid-19 vaccines for domestic flights, the nation's top infectious disease expert said Monday.

"When you make vaccinations a requirement, that's another incentive to get more people vaccinated," said Dr. Anthony Fauci in an interview on MSNBC's "Morning Joe." "If you want to do that with domestic flights, I think that's something that seriously should be considered."

There is no indication at this point that a vaccine mandate is on its way for U.S. flights. When asked on MSNBC, Fauci, White House chief medical advisor, declined to say whether he has made the recommendation to President Joe Biden.

The White House, when asked for comment, referred CNBC to Biden's statement to ABC News last week, "It's been considered," Biden said, "but the recommendation I've gotten, it's not necessary."

The travel industry, meanwhile, expressed opposition to a vaccine mandate for domestic travel when Fauci made a similar suggestion in September.

Later on Monday, Fauci said he didn't think a mandate would be imposed any time soon.

"Right now, I don't think people should expect that we're going to have a requirement in domestic flights for people to be vaccinated," he told CNN. "When I was asked that question, I gave an honest answer. It's on the table, and we consider it. But that doesn't mean it's going to happen. I doubt if we're going to see something like that in the reasonably foreseeable future."

Already, U.S. passengers must wear masks to board planes and keep them on for the duration of the flight except when eating or drinking.

International travelers must also show proof of vaccination and a negative Covid test in order to board a U.S.-bound flight, and also wear a mask.

With the omicron variant of the coronavirus spreading rapidly across the U.S., airlines have canceled more than 2,000 flights since Friday, due partly to outbreaks among staff.

Across the country, omicron accounts for the majority of new infections, at 73% of fresh cases as of last Monday. The highly infectious variant has caused a handful of states, including New Jersey and New York, to report more coronavirus cases than in any other seven-day period since the start of the pandemic.

A handful of cities in the U.S., including New York City, require proof of vaccination to attend in-door venues such as Broadway theaters, sports arenas, restaurants and fitness centers.