WATCH: White House COVID task force holds briefing as vaccine makers seek approval for boosters

U.S. manufacturers of COVID-19 vaccines are seeking additional approvals from federal regulators in order to distribute and administer more booster shots for at-risk Americans and first doses for children ages 5 to 11.

Watch the event in the player above.

With many Americans who got Pfizer vaccinations already rolling up their sleeves for a booster shot, millions of others who received the Moderna or Johnson & Johnson vaccine wait anxiously to learn when it’s their turn.

Federal regulators begin tackling that question this week.

Jeffrey Zients, the White House COVID Response Coordinator, said the U.S. booster shot program is “off to a very strong start and continues to accelerate.”

“By the end of today, we estimate that over seven million Americans will have gotten their booster shot, including about three million just in the last week,” Zients said. “And importantly, in less than three weeks, more than one in three eligible seniors have already gotten their third shot.”

On Thursday and Friday, the Food and Drug Administration convenes its independent advisers for the first stage in the process of deciding whether extra doses of the Moderna and J&J vaccines should be dispensed and, if so, who should get them and when. The final go-ahead is not expected for at least another week.

READ MORE: FDA now begins to look at approving Moderna and Johnson & Johnson boosters

After the FDA advisers give their recommendation, the agency itself will make a decision on whether to authorize boosters. Then next week, a panel convened by the Centers for Disease Control and Prevention will offer more specifics on who should get them. Its decision is subject to approval by the CDC director.

U.S. Surgeon General, Dr. Vivek Murthy, said the process is meant to bolster public confidence in the vaccines.

“All of these layers of review the thousands of pages of data, the expert committees and the fact that this is open to the public, they should all bolster our confidence that we have a rigorous, independent and transparent review process for vaccines in our country,” Dr. Murthy said.

But the review process has already led to conflicts among experts and agencies — and documents the FDA released Tuesday suggest this week’s decisions will be equally difficult.

Pfizer is also seeking additional U.S. authorization for it’s COVID-19 vaccine which it says works for children ages 5 to 11.

The vaccine is already is available for anyone 12 and older. But with kids now back in school and the extra-contagious delta variant causing a huge jump in pediatric infections, many parents are anxiously awaiting vaccinations for their younger children.

WATCH: Vaccine mandates can become a ‘political battleground,’ former FDA commissioner says

According to Dr. Murthy, advisory committees with the FDA and CDC could release their decisions on the pediatric vaccines by early November.

For elementary school-aged kids, Pfizer tested a much lower dose — a third of the amount that’s in each shot given now. Yet after their second dose, children ages 5 to 11 developed coronavirus-fighting antibody levels just as strong as teenagers and young adults getting the regular-strength shots, Dr. Bill Gruber, a Pfizer senior vice president, told The Associated Press.

Zients says the White House is already reaching out to states to start educational campaigns for the different type of the Pfizer vaccine meant for kids.

“We’ll bring that vaccine, as we’ve talked about, to pediatricians offices also directly to schools where appropriate and to community sites,” Zients said. “And we’ll work with trusted messengers as we have throughout, particularly those trusted messengers who can answer questions for parents and kids. So we’ll make it convenient and easy for parents and kids to get vaccinated. We have the supply and we will be ready.”

Support PBS NewsHour: