Speaking to CNN correspondent Dana Bash during his latest State of the Union appearance, the leading health expert addressed potential impacts of indoor gatherings and widespread travel tied to holiday celebrations. Acknowledging the present spike in virus cases and grave fatality toll that has climbed in conjunction with it, Fauci said a “post-seasonal” surge could materialize near the start of 2021.

“The reason I’m concerned, and my colleagues in public health are concerned, also, is that we very well might see a post-seasonal—in the sense of Christmas and New Year’s—surge,” said the top physician and longstanding director of the National Institute of Allergy and Infectious Diseases (NIAID). “Because if you look at the slope…the incline of cases that we’ve experienced as we’ve gone into the late fall and soon-to-be early winter, it is really quite troubling.”

Fauci echoed remarks from President-elect Joe Biden prior to Christmas last week, telling Bash, “as we get into the next few weeks, [the outbreak] might actually get worse.” He pinpointed the heightened incidence of in-person social events and movement as the cause of this anticipated surge.

Numerous public officials, including Fauci, previously urged U.S. residents to celebrate the holidays virtually, or limit in-person gatherings to small groups, as means to reduce risks of exacerbated COVID-19 transmission. On Wednesday, Biden reminded Americans that “our darkest days in this battle against COVID are ahead of us — not behind us,” and implored civilians to exercise particular caution and adhere to safety measures in preparation.

However, despite their recommendations, as well as formal guidance released by the Centers for Disease Control and Prevention (CDC), many people proceeded with their holiday usual plans. Last Wednesday marked the busiest day of U.S. air travel since the pandemic began, with data from the Transportation Security Administration (TSA) confirming nearly 1.2 million passenger screenings at airports across the country. Wednesday’s airport traffic followed days of rising numbers. TSA records showed at least 4 million additional passengers were screened at airport security checkpoints since the previous weekend.

Close to 19 million people have tested positive for COVID-19 in the U.S. as of Sunday morning, and roughly 332,000 people have passed away as a result, according to Johns Hopkins University’s data.

Fauci also shared details about his experience receiving the first installment of a two-dose COVID-19 vaccine during his State of the Union appearance on Sunday. The NIAID director was vaccinated on camera, as were other public figures who received the early immunization. He reported experiencing minimal side effects.

Newsweek reached out to NIAID for further comment, but did not receive a reply in time for publication.