The Transportation Security Administration (T.S.A.) screened more than 1.28 million commercial airline passengers on Sunday, the busiest day for U.S. airports since mid-March, when the nation's coronavirus outbreak crippled travel demand. Airline travel demand has been slowly increasing into the year's end despite alarmingly high levels of nationwide infections.

About 5.7 million airline passengers passed through T.S.A. checkpoints between Dec. 23 and Dec. 27 as Americans traveled for the holidays, with three of those days totalling over one million. T.S.A. daily screening totals have only exceeded one million 11 times since the pandemic began, usually occurring around holidays.

However, daily screenings are still below their 2019 levels, with this past five day volumes being about 53% lower than last year's roughly 12 million travellers.

National airline traveling volumes continue to increase despite the Centers for Disease Control and Prevention earlier recommendations for Americans postpone their holiday traveling and keep their celebrations to just household members as cases continue to rise.

Dr. Anthony Fauci, the nation's top infectious disease expert, expressed concern on Sunday over the state of the country's ongoing battle with the coronavirus, echoing President-elect Joe Biden's forecast that the "darkest days" of the pandemic are ahead.

"The reason I'm concerned and my colleagues in public health are concern also is that we very well might see a post-seasonal, in the sense of Christmas, New Year's, surge, and, as I have described it, as a surge upon a surge, because, if you look at the slope, the incline of cases that we have experiences as we have gone into the last fall and soon-to-be-early winter, it is really quite troubling," Fauci told CNN's Dana Bash on "State of the Union."

"I share the concern of President-elect Biden that as we get into the next few weeks, it might actually get worse."

Airline Relief

U.S. airlines are set to receive $15 billion in additional payroll assistance under Congress's new coronavirus relief bill which President Donald Trump signed into law on Sunday. The new round of funding would require American Airlines (AAL  ) and United Airlines (UAL  ) to return their more than 32,000 furloughed employees back to payrolls.

Airlines throughout the pandemic have cut employee levels through programs like voluntary leave and early retirement deals to avoid furloughs. With the passage of the new stimulus package, Southwest Airlines (LUV  ) Chief Executive Officer Gary Kelly told employees that the airline is halting its previous plan to furlough about 7,000 workers, adding that the airline does not expect any needs for job or pay cuts throughout 2021.