(NEW YORK) — Vaccines for children will “very likely” be available the first or second week of November, White House Chief Medical Adviser Dr. Anthony Fauci said Sunday.

“If all goes well, and we get the regulatory approval and the recommendation from the CDC [Centers for Disease Control and Prevention], it’s entirely possible if not very likely that vaccines will be available for children from 5 to 11 within the first week or two of November,” Fauci told ABC This Week anchor George Stephanopoulos.

Pfizer’s COVID-19 vaccine is nearly 91% effective against symptomatic illness in children ages 5-11, according to new data. A Food and Drug Administration advisory panel will meet Tuesday to discuss authorizing the vaccine for children, which is currently only available to those ages 12 and older.

The CDC issued recommendations for both Moderna and Johnson & Johnson vaccine boosters for certain populations on Thursday evening, clearing the way for millions of Americans to receive additional shots. The CDC’s authorization followed the FDA’s, which it issued Wednesday.

The CDC is also permitting mix-and-match booster doses — allowing people to get a different booster brand than was used for a primary vaccination.

Fauci said Sunday the new recommendations should not cause confusion, as they allow for flexibility in booster selection.

“We would hope that people, if available, would get the boost from the original product,” Fauci said. “But if not, there’s the flexibility of what we’re calling ‘mixing and matching."”

Stephanopoulos pressed Fauci on whether receiving a different brand shot from the original dose yields better protection.

“I have read some studies that suggest that it’s actually better to mix. Like, say, if you got the Johnson & Johnson the first time around, it’s better to get Moderna the second time,” Stephanopoulos asked.

“If you look at the level of antibodies that are induced — if you originally had J&J, and you get, for example, a Moderna or a Pfizer, the level of antibodies, namely, the proteins that you would predict would protect you, those levels go up higher with the Moderna boost to J&J than the J&J boost,” Fauci responded. “However, it’s a little bit more complicated, because, in the clinical trial that J&J did, the clinical effect of the second dose of J&J was quite substantial.”

“So, it really becomes an issue of, what’s the most convenient? What do you feel is best for you?” Fauci added, recommending that people consult their physician.

Stephanopoulos also pressed Fauci on the controversy over to what extent the U.S. was funding bat coronavirus research in Wuhan after the NIH released a letter this week about a New York City-based nonprofit’s research on bat coronavirus spike proteins. The letter states that the subcontractor had not disclosed some results in a timely manner.

“Now, some critics and analysts have seized on that to say you and others have misled the public about U.S. funding of this so-called gain-of-function research. The NIH says that’s false. Our medical unit backs that up,” Stephanopoulos said. Sen. Rand Paul, R-Ky., has called for Fauci’s firing over the controversy.

“Well, I obviously totally disagree with Senator Paul. He’s absolutely incorrect. Neither I nor Dr. Francis Collins, the director of the NIH lied or misled about what we’ve done,” Fauci responded.

“What did we learn from the letter? Does it show that some of the research we were finding was riskier than we know?” Stephanopoulos pressed.

Fauci said they knew what the risk was and there’s “no denial” that they should have put their progress report in a timely manner, but that the implication that the research led to COVID-19 is “unconscionable” and “molecularly impossible.”

“There’s all of this concern about what’s gain-of-function or what’s not, with the implication that that research led to SARS-CoV-2, and COVID-19, which, George, unequivocally anybody that knows anything about viral biology and phylogeny of viruses know that it is molecularly impossible for those viruses that were worked on to turn into SARS-CoV-2 because they were distant enough molecularly that no matter what you did to them, they could never, ever become SARS-CoV-2,” Fauci explained.

“And yet when people talk about gain-of-function, they make that implication which I think is unconscionable to do, to say, ‘Well, maybe that research led to SARS-CoV-2’,” Fauci added. “You can ask any person of good faith who’s a virologist, and they will tell you, absolutely clearly, that that would be molecularly impossible.”

Copyright © 2021, ABC Audio. All rights reserved.