• Pfizer said it asked the FDA to authorize booster shots of its Covid-19 vaccine for all Americans age 18 and older.
• If approved, it would significantly increase the number of people eligible to get the extra shots.
• A third dose of the vaccine has already been authorized for elderly people and at-risk adults six months after they complete their primary series of shots.

Pfizer said Tuesday it asked the Food and Drug Administration to authorize booster shots of its Covid-19 vaccine for all Americans age 18 and older, a move that would significantly increase the number of people eligible to get the extra shots.

A third dose of the vaccine, which was developed with German partner BioNTech, has already been authorized by the FDA for elderly people and at-risk adults six months after they complete their primary series of shots.

Booster shots of Moderna's vaccine have also been cleared for the same groups as Pfizer's while a second shot of Johnson & Johnson's has already been cleared for all adults. More than 25 million Americans have received an additional dose of one of the three vaccines as of Monday, according to data compiled the Centers for Disease Control and Prevention.

Pfizer said Tuesday it is asking the agency to amend its authorization after data based on more than 10,000 individuals shows an additional dose is safe and effective.

The FDA could grant Pfizer's request before Thanksgiving, the New York Times reported, citing unnamed sources.

Booster shots have been a contentious topic for scientists — in and outside the government — especially as many people in the U.S. and other parts of the world have yet to receive even one dose of a vaccine. The World Health Organization is urging wealthy countries to hold off on distributing boosters. Some scientists say they aren't convinced most Americans need boosters right now.

President Joe Biden in August said he wanted to roll out boosters shots to all adults as early as September. However, an influential FDA advisory committee later rejected that proposal, paring back those plans to unanimously recommend the third shots to people age 65 and older and other vulnerable Americans.

Speaking with CNBC's Andrew Ross Sorkin at the DealBook Online Summit, Bourla declined to provide a prediction for when he thought boosters for everyone 18 and older could be authorized, leaving it up to federal regulators.

He said he felt boosters should have been recommended for all adults and some teens back in September, but he added that it was not for him to decide. The company asked the agency in August to authorize boosters for everyone 16 and older. However, some FDA advisors raised concerns about the risk of myocarditis in younger people, saying more research is needed.

"The FDA felt at the time .. that they should give it to 65 and above and 18 all the way to 65, only to those that had high exposure," he said.