Top U.S. health officials on Friday urged Americans to get COVID-19 vaccine boosters if eligible to help ward off infections during the holiday season.

Speaking at a virtual town hall, White House COVID-19 Response Coordinator Dr. Ashish Jha suggested people who had been infected with COVID in September or earlier consider getting an anti-Omicron booster shot.

The shots, made by Pfizer Inc (PFE.N), BioNTech SE (22UAy.DE) and Moderna Inc (MRNA.O), have been available since September, but Americans have not been rushing to get them.

Around 42.2 million of the updated shots have been given in the United States so far, with just 34% of Americans aged 65 or older getting injected.

“Don’t wait. If you wait you put yourself at risk,” said Dr. Anthony Fauci, chief medical advisor to the president. “If you’re up to date, great. If not, get vaccinated.”