Fauci, who heads the United States' National Institute of Allergy and Infectious Diseases, addressed Santa Claus' health during a CNN/Sesame Street Town Hall for Families.
"How does Santa get the vaccine, and is it safe for him to go in the house?," asked Lucy, age 8, of San Rafael, Calif.
Another child, Paxton, 6, of Geneva, Ill., asked if Santa would still be able to visit him this season.
"What if he can't go to anyone's house or near his reindeer?" Paxton asked.
Fauci told Elmo and his friends he anticipated their concerns, and he took care of it.
"I took a trip up there to the North Pole," Fauci said. "I went there, and I vaccinated Santa Claus myself. I measured his level of immunity, and he is good to go. He can come down the chimney. He can leave the presents, he can leave, and you have nothing to worry about."
Amid the COVID-19 pandemic and racial justice movement, CNN and Sesame Street have collaborated on five Town Halls for children this year.
The North American Aerospace Defense Command, NORAD, has also planned to continue its annual tracking of Santa's journey around the world on Christmas Eve as it has done every year since 1955.