▶ Watch Video: States shedding mask mandates over new CDC guidelines

Washington — Dr. Anthony Fauci, chief medical advisor to President Biden, said Sunday that updated mask guidance for Americans who are fully vaccinated against COVID-19 was “based on the evolution of the science” as the Centers for Disease Control and Prevention (CDC) learned more about the real-world effectiveness of the shots.

“The underlying reason for the CDC doing this was just based on the evolution of the science,” Fauci said in an interview with “Face the Nation” on last week’s announcement. “But if in fact this serves as an incentive for people to get vaccinated, all the better. I hope it does actually.”

The CDC said Thursday that anyone who is fully vaccinated can shed their masks and forgo social distancing for most indoor and outdoor activities, regardless of gathering size, marking a substantial return to normalcy in the long fight against the coronavirus pandemic. In the wake of the new guidance from the health agency, the White House lifted its own mask requirement for fully vaccinated staff.

While the new guidance from the CDC was largely celebrated, it did bring some confusion, as the agency said last month Americans who have been fully vaccinated against the coronavirus were still safer wearing masks in crowded outdoors settings and inside.

Fauci said three factors drove the change from health officials: an accumulation of data showing the “real-world effectiveness” of the vaccines, which are more than 90% effective in protecting against disease; new studies showing the vaccines protect against the new coronavirus variants; and information showing it’s unlikely a vaccinated person who becomes infected witch the coronavirus transmits it to someone else.

“The accumulation of all of those scientific facts, information and evidence brought the CDC to make that decision to say now when you’re vaccinated, you don’t need to wear a mask, not only outdoors, but you don’t need to wear it indoors,” he said.

Fauci said he expects the CDC will release more specific guidance in the coming weeks about the need for mitigation measures for fully vaccinated people in particular settings, like the workplace.

While there is the possibility that people who have been vaccinated can test positive for the coronavirus, as evidenced by the eight vaccinated members of the New York Yankees who contracted the virus, Fauci said the likelihood of it spreading is “very, very low.”

“What the issue is, is that the level of virus in your nasal pharynx, which is correlated with whether or not you were going to transmit it to someone else, is considerably lower,” he said. “So even though there are breakthrough infections with vaccinated people, almost always the people are asymptomatic, and the level of virus is so low, it makes it extremely unlikely, not impossible, but very, very low likelihood that they are going to transmit it.”

Nearly 47% of the adult population in the U.S. is fully vaccinated, according to the CDC, and nearly 60% of the adult population has received at least one dose. The vaccination rate is expected to increase following the Food and Drug Administration’s authorization this week for use of Pfizer’s two-dose shot in adolescents between the ages of 12 and 15.

The CDC reported 43.5% of the population over the age of 12 is fully vaccinated. 

As supply of the vaccines has outpaced demand, the Biden administration has rolled out new incentives designed to boost vaccination rates, including partnering with ridesharing companies Uber and Lyft for free rides to vaccination sites, and offering a tax incentive to some businesses who offer paid leave for employees to get their shots and recover from side effects.

Fauci said the data also indicates getting vaccinated against the coronavirus serves the public’s interest as well.

“When you get vaccinated, you not only protect your own health and that of the family, but also you contribute to the community health by preventing the spread of the virus throughout the community,” he said. “In other words, you become a dead-end to the virus.  And when there are a lot of dead ends around, the virus is not going to go anywhere.”