The U.S. Transportation Security Administration (TSA) said it screened 1.63 million passengers on Sunday at U.S. airports, the highest number since March 2020, when the coronavirus pandemic slashed travel demand.

The number of U.S. air travelers is still about 35% lower than the same date in 2019, down about 1 million travelers, the TSA said. By comparison, just 170,000 people were screened at U.S. airports on the same day in May 2020. U.S. airlines have been adding more flights, anticipating rising summer travel demand.

Last month, United Airlines said it was adding more than 480 daily flights to its U.S. schedule in June to meet summer travel demand that is expected to rise as more people receive COVID-19 vaccines.

The company said it plans to fly 67% of its domestic schedule and 60% of its overall schedule compared with June 2019.

American Airlines said in April it expects to fly more than 90% of its domestic seat capacity compared with summer 2019 and 80% of its international seat capacity compared with 2019, and it will operate more than 150 new routes this summer.

Airlines are seeing an uptick in bookings as accelerated vaccination efforts encourage leisure travel with friends and family after months of pandemic-linked restrictions.