Some aides argued that other countries already require vaccinations to fly and that the United States should join their ranks, according to an administration official. But others said mandates work best when they require people to prove they are immunized only once - like at work - rather than repeatedly, like every time they board a plane.
The idea was shelved, but top White House officials say that proposal and similar ones are still under consideration - including, potentially, a broader vaccine mandate that would include domestic air travel.
"We're discussing it," Anthony Fauci, President Joe Biden's chief medical adviser, said about the idea of a broader requirement in an interview. "It's on the table for discussion."
White House officials stressed that no additional mandates are imminent, as the Biden administration is still sorting through how to implement the ones announced last week.
The debate over an airplane mandate, which many public health officials say is a logical next step, highlights Biden's struggle to balance public health needs with practical, economic and political considerations. Some at the White House warn, for example, that an air mandate could prompt frustratingly long lines at airports.
Either way, Biden's top advisers say that significantly more measures may be needed to convince - or coerce - Americans to get vaccinations, as more than 70 million Americans who qualify for coronavirus shots have not gotten them.
That could mean more social tumult ahead, since Republicans are increasingly embracing a no-mandate message. GOP governors have announced lawsuits to block last week's actions, and House Minority Leader Kevin McCarthy, R-Calif., on Monday tweeted, "NO VACCINE MANDATES."
Requiring vaccines for air travel would be a big step beyond Biden's announcement last week that businesses with more than 100 employees must require their workers to get vaccines or regular tests. Biden also ordered all federal employees to get shots and said most health care facilities that get Medicare or Medicaid funding will now have to immunize their workers.
In a departure for the disciplined Biden White House, some of the disagreements about an air travel mandate have broken into the open. Fauci, for example, applauded the idea in an interview for The Skimm podcast, saying, "I would support that if you want to get on a plane and travel with other people, that you should be vaccinated."
But in a different podcast, "Pod Save America," White House Chief of Staff Ron Klain challenged the notion, suggesting it's impractical and possibly unnecessary. "We're going to pick up the vast majority of Americans with the requirements we've [already] put in place," Klain said.
Still, he added that the air travel mandate "is something we continue to look at."
One person who talks regularly with White House officials said they often seem overwhelmed with the sheer number of anti-covid proposals being tossed at them from various quarters.
Mandates are only one of the anti-covid measures the White House is juggling. The administration moved this week to stave off shortages of monoclonal antibodies, taking over distribution of the critical covid-19 therapy and purchasing 1.4 million additional doses.
That change, which took effect Monday, is all but certain to result in cuts to some states, especially seven in the Deep South with high infection rates that have been using about 70% of the national supply.
Soaring demand for the therapy represents a sharp turn from just two months ago, when monoclonal antibodies were widely available. Since then, word of the highly effective therapy - which is free to patients - has spread, with federal officials and Republicans, including Florida Gov. Ron DeSantis, urging their use.
So the Department of Health and Human Services will, at least temporarily, set the rules for their distribution instead of allowing states, medical facilities and doctors to order them directly. "HHS will determine the amount of product each state and territory receives on a weekly basis," an HHS spokesman said.
The issue of a potential vaccine requirement for air travel arose several weeks ago, during an administration discussion of whether to extend the current airplane mask mandate. Some advisers suggested that - besides masking up - international travelers be required to prove they had been vaccinated or tested negative, according to a person familiar with the conversation who spoke on the condition of anonymity because they were not authorized to describe it.
It is unclear whether the policy would apply to Americans traveling abroad, to foreigners visiting the United States, or both.
There was also a discussion of whether a mandate for domestic flights might also be necessary, the person said. But some administration officials challenged that idea, asking how the rule would apply in emergency situations, or if an unvaccinated traveler was headed to a funeral and had no time to get inoculated.
The White House has also been contending with pushback from the airline industry to the idea of further domestic mandates.
Industry officials have told the administration that they've already been hit hard by the pandemic and contended that air travel is now a relatively safe activity, because airlines are requiring masks and have increased airflow in the cabin in response to the pandemic.
"A4A passenger carriers comply with all [Centers for Disease Control and Prevention] guidelines and requirements, and remain committed to leaning into science to guide policies and protocols that prioritize the well-being of all travelers and employees," said Katherine Estep, a spokeswoman for Airlines For America, an industry trade group.
Fauci suggested it made sense for Biden to consider an array of issues, including the likely reaction to a policy, in deciding what anti-covid steps to take. "The president has to make decisions based on a number of factors - the acceptance of it, the impact of it, what the response would be of it," Fauci said.
One question the administration has so far stayed away from is what constitutes an acceptable proof of vaccination, an issue that seems central to any mandate. The administration has said it will not create vaccine "passports" or ID cards but has not specified what kind of evidence employers should require instead.
U.S. vaccination rates began to tick up recently after weeks of stagnation as the delta variant surged and more people feared infection. But they are still nowhere near where they were in the spring, when more than 3 million people a day were getting shots, according to a Washington Post vaccine tracker.
Mandates have been shown to be perhaps the most effective tool to compel hesitant people to get vaccinated, and several European countries saw vaccination figures rise after they instituted mandates for activities like going to restaurants, bars and gyms. There is a growing consensus among public health experts that Biden will similarly have to go further.
"What they did is fantastic, don't get me wrong," said Ezekiel Emanuel, a bioethicist at the University of Pennsylvania who was on Biden's transition team. "But unfortunately we need more, because there are lots of people who will fall through the cracks with what's been done."
He added, "The easiest and best thing to do at this point is probably a travel mandate."
White House officials stress that since they announced a major package of mandates just last week, they are focused on implementing those before they add new ones. "Right now, our focus is on operationalizing this plan as quickly and effectively as possible," said Kevin Munoz, a White House spokesman.
But other officials leave little doubt that other actions could come. "We're not taking any measures off the table," Jeff Zients, the top White House covid-19 response coordinator, said Friday.
Zients suggested that the White House prefers prodding private companies to require vaccines, as in last week's mandates, rather than implementing mandates itself, as it would have to do for air travel. The more visible the government is in enforcing mandates, he said, the more likely it to antagonize vaccine resisters.
"We believe that workplaces are a very efficient and effective way to ensure that people get vaccinated or, at minimum, get tested one time per week," Zients said. "And verifying in the workplace that someone is vaccinated does not place an ongoing burden on vaccinated people."
Similarly, the White House has urged the nation's governors to enact various mandates, including one for teachers, school staffers and students 12 and older.
Some critics have accused Biden of being too slow to use the levers available to him to require that all Americans get vaccines, given how quickly the pandemic would end if more people took them. But others say the president was right to calibrate his actions to the public's sentiment, which has grown more supportive of mandates.
"You go incrementally. You build up towards mandates," said Celine Gounder, an epidemiologist who was a member of Biden's covid task force during the transition. "You need to show that less-aggressive approaches are not working before you go to a more aggressive approach."
Gounder said she has told administration officials that if they impose a travel mandate, they should make sure vaccines are available at travel hubs so that the unvaccinated can get shots there. Such a scenario would envision a travel mandate where Americans would not have to be fully vaccinated to travel, since a second shot comes several weeks later.
Other countries have been more willing than the U.S. to impose far-reaching mandates. In France, vaccines are mandatory for health care workers and patrons of restaurants, bars, museums and other public venues will be required to present a "health pass" demonstrating they are fully vaccinated, have a negative test or have recovered from the virus.
French officials, who forged ahead despite protests, have reported a surge in vaccine appointments after announcing the mandates. In the European Union in general, more than 70% of the population is fully vaccinated.
Even before Biden's sweeping mandates were announced last week, some businesses in the United States had instituted mandates or penalties for those who do not get vaccinated. Delta Air Lines, which last month said employees who do not get vaccinated will have to pay $200 more per month for their health care, said a fifth of its unvaccinated employees received shots within two weeks of the company's announcement.
Tyson Foods said 5,400 workers received their first coronavirus shots or were fully vaccinated about a week after it announced its workforce had to be inoculated by November.
The administration still must write a rule to implement Biden's new policy that firms with more than 100 employees must require vaccines or regular testing. The rule will also almost certainly face legal challenges from Republicans who have said they will sue the administration.
Klain, speaking on the "Pod Save America" program, said he is confident the move will survive legal scrutiny, saying it is a "very standard application" of the authority of the Occupational Safety and Health Administration.
He compared it to the rule that construction workers must wear hard hats. "We're in a pandemic right now," Klain said. "To keep workers safe, to keep people in the workplace safe, requiring vaccinations is part of OSHA's mandate."