Washington D.C. - With the US health care system already under immense strain due to high hospitalization numbers, the country's top infectious diseases expert Anthony Fauci has warned of a likely sharp post-holiday spike in new coronavirus cases.

"We are really at a really critical point," Fauci told CNN on Sunday, referring to the health care system. On an average day, some 120,000 people were in hospital across the US with Covid-19 complications, he noted.

On Christmas Eve, the country recorded 2,938 additional virus-related deaths, according to the Covid Tracking Project.

Despite warnings against travelling for Christmas, people had been packing airports and taking to the roads, Fauci said, prompting his concern about a "surge" in infections after the holiday season.

On Wednesday, the country set a single-day air travel record since the start of the pandemic, when nearly 1.2 million people took flights, according to federal government data.

Fauci continued to urge people to get vaccinated when they can, even as he acknowledged that the roll-out started earlier this month had been slow. Governors have complained of problems in the logistical chain that have delayed inoculation plans.

Fauci projected that the general population will start to get vaccinated by April and that the country could see a return to some kind of normality by autumn.

The Trump administration's forecast for the vaccine roll-out is a bit brighter, with a prediction of mid-summer for the country to reach herd immunity.