The U.S. Food and Drug Administration on Thursday expanded emergency-use authorization for a booster dose of the Pfizer-BioNTech COVID-19 vaccine to include teens who are currently 16 and older. The Centers for Disease Control and Prevention will also have to approve boosters for 16- and 17-year-olds, which could happen as soon as Thursday, according to the Washington Post. More than 2.3 million teens in that age group received their second dose of Pfizer’s vaccine at least six months ago, according to the CDC.

Thursday’s approval follows the decision last month by the FDA to allow all adults 18 and older to get a booster dose of the Moderna and Pfizer vaccines. Currently, about 24% of Americans over the age of 18 have received a COVID-19 vaccine booster, according to the CDC.

Pfizer, which filed for FDA approval for its booster for 16- and 17-year-olds at the end of November, said the FDA’s approval was a “critical milestone” in the continuing fight against COVID. “From the beginning, we aimed to provide strong, safe protection to as many people as possible in an effort to end this pandemic. While new variants, including Omicron, emerge across the globe, we believe that the best way to minimize the spread of COVID-19 and any future variants is getting all eligible people fully vaccinated with the first two-dose series and a booster dose as recommended,” Pfizer’s CEO Albert Bourla said in a statement. 

Last month, the CDC updated its stance on boosters, urging all adults to get a booster shot. Currently, officials are recommending Americans who had two doses of Moderna’s or Pfizer’s vaccine get a booster six months after their last vaccine dose. Those who received a Johnson & Johnson vaccine should get a booster after two months. 

As the highly contagious Omicron and Delta variants of COVID continue to spread, recent studies have shown that a third dose of Pfizer’s COVID-19 vaccine can help fight off infections better than just two doses.  

“The booster vaccination increases the level of immunity and dramatically improves protection against COVID-19 in all age groups studied so far,” said Dr. Ugur Sahin, CEO and cofounder of BioNTech. “In the current situation, it is important to offer everyone a booster, particularly against the background of the newly emerging variants such as Omicron.” 

“Getting fully vaccinated and having your booster on board is a major wall against this virus in terms of what it does to you,” Michael Osterholm, a leading epidemiologist and director of the Center for Infectious Disease Research and Policy at the University of Minnesota, recently told Fortune. For instance, while the available COVID vaccines may have lower protection rates against Delta infections, it does generally prevent severe hospitalization and death. Omicron seems to be following a similar path.