More than 1.3 million people moved through U.S. airport security checkpoints Sunday — the most since the beginning of the coronavirus pandemic, the Transportation Security Administration announced Monday.

The number was far below what it was on the same day in 2019, when more than 2.4 million people were screened. Still, the increase came despite recommendations by the Centers for Disease Control and Prevention and local health officials that people not travel during the holiday season.

It also came as the U.S. death toll from the virus surpassed 350,000 on Sunday, according to data compiled and reviewed by The Washington Post.

During the first three days of January, the TSA screened more than 3.3 million people. Roughly 1.2 million people moved through TSA checkpoints Saturday before the record the next day.

December also saw an increase in airport traffic, with the number of people screened surpassing 1 million on nine days.

The agency recorded similar upticks in November. On the Sunday after Thanksgiving — traditionally one of the busiest travel days of the year — more than 1.1 million people were screened, compared with 2.8 million in 2019. In November, screening volumes exceeded 1 million on four days during the Thanksgiving travel period.

Whether those trips will fuel a surge in infections is something officials are watching.

“For the past nine months, we have been reminding people of best practices to reduce the risks of spreading covid-19,” said Craig Fifer, a spokesman for the city of Alexandria, Va. “Anything that disregards those best practices can potentially increase the spread. While there are ways to reduce the risks of travel, there are still inherent risks of transmission.”

Despite the recent rise in airport screenings, the industry will close out the year with far lower numbers than in 2019. In all, TSA officers screened 324 million passengers in 2020, compared with 824 million in 2019, a decrease of more than 60 percent.

Passenger volumes have slowly increased and are significantly higher than in the spring, when communities grappled with how to manage the first wave of infections. The TSA recorded the lowest number of screenings on April 14, when 87,500 people were screened nationwide. The agency expects volumes to continue to mirror traditional travel patterns with upticks around holidays and traditional getaway periods such as spring break. Officials said numbers will probably remain well below pre-pandemic levels for most of 2021.

In a briefing last week, Montgomery County (Md.) Health Officer Travis Gayles said he was aware of reports of more people flying during the holidays but said it is unclear whether those trips will result in a surge in cases. He said an “unknown factor” is how people behaved during and after their trips, such as whether they wore masks.

The TSA, airports and airlines have adopted measures to slow the spread of the coronavirus, including requiring people to wear masks and to practice social distancing.

The agency has installed nearly 7,000 acrylic barriers at 384 airports across the country, as well as more than 900 machines that allow passengers to scan their own IDs, eliminating the need to hand it to a TSA officer. Reagan National Airport is among the 125 locations where the self-serve Credential Authentication Technology units are in use.

Even so, the TSA’s workforce has not been immune from the virus. More than 5,000 employees have tested positive for the coronavirus. While more than 4,300 have recovered, 12 have died. Currently, 851 employees have active infections and are isolating, the agency said.

Many airports and airlines offer travelers the option of being tested before they board their flights. In early December, the CDC updated its guidelines to encourage people to be tested one to three days before they depart, and again three to five days after returning.

Health officials, however, continue to caution that even if a person tests negative for the virus, the result represents only a single point in time, and individuals must continue to wear a mask, wash their hands and physically distance from others.

Rebecca Tan contributed to this report.