Dr. Anthony Fauci, the nation’s top infectious disease doctor, said in an interview with the theSkimm that he would support a vaccine mandate for air travelers.

“I would support that if you want to get on a plane and travel with other people, that you should be vaccinated,” Dr. Fauci told the site, which targets millennial women.

Dr. Fauci’s support for such a mandate follows President Biden’s recent announcement that all companies with 100 or more workers will require vaccination or weekly testing.

The sweeping actions from Mr. Biden reflect his frustrations with the roughly 80 million Americans who are eligible for shots but remain unvaccinated. Mr. Biden also moved to mandate vaccinations for health care workers, federal contractors and the vast majority of federal workers, who could face disciplinary measures if they refuse.

The president also said that the Transportation Security Administration would double fines on travelers who refused to wear masks.

When asked on Friday if the administration was considering vaccine or testing requirements for domestic flights, Jeff Zients, Mr. Biden’s coronavirus response coordinator, told reporters that they were “not taking any measures off the table.”

Some airlines, such as United Airlines and Frontier Airlines, have required that all U.S. employees get vaccinated. Delta has intensified pressures for employees to get vaccinated but has stopped short of a mandate.