The nation’s top infectious-disease expert, Anthony S. Fauci, said Monday the United States should consider a vaccination requirement for domestic air travel amid a surge in coronavirus cases that has contributed to days of disruptions for airlines that are missing crew members.

While noting that there were pros and cons to such a move, Fauci said it was “just another one of the requirements that I think is reasonable to consider,” along with similar requirements at some universities and workplaces.

“That’s another incentive to get more people vaccinated,” he said during an appearance on MSNBC. “If you want to do that with domestic flights, I think that’s something that seriously should be considered.”

Fauci, who acts as President Biden’s chief medical adviser, said in September he would support a vaccine mandate for U.S. flights. Sen. Dianne Feinstein (D-Calif.) and Rep. Don Beyer (D-Va.) have introduced legislation that would add a vaccine requirement to U.S. airways and trains to no avail. In November, Transportation Secretary Pete Buttigieg cited other strategies for stopping the coronavirus, including masking and vaccinating travel industry workers, as “highly effective,” but that was before the discovery of the highly transmissible omicron variant.

More than a thousand flights within or going to or from the United States had been canceled as of midday Monday, according to the flight-tracking company FlightAware, following a Christmas weekend marked by travel troubles. About 1,500 U.S. flights were canceled Sunday and an additional 997 Saturday, the service said. Industry experts have stressed that the recent cancellations and delays are small compared with the meltdowns airlines sustained over the summer, but more volatility should be expected until the omicron-fueled wave subsides.

Airlines have blamed staffing shortages prompted by employees who tested positive for the coronavirus. Cases are skyrocketing amid the rise of the highly contagious omicron variant, and Centers for Disease Control and Prevention guidelines call for those infected with the virus to isolate for 10 days. Leaders of major U.S. airlines have called on the agency to cut that time in half.

One airline, Delta, said the combination of winter weather and the omicron surge had created “a perfect storm.” In a news release Monday, the company said upward of 200 flight cancellations were expected — more than the 40 forecast a day earlier. JetBlue said in an emailed statement it had seen an increasing number of sick calls from the variant. The company had canceled 66 flights as of midday.

“Despite our best efforts, we’ve had to cancel a number of flights,” JetBlue said, “and additional flight cancellations and other delays remain a possibility as we see more omicron community spread.”