(WTVO) — The U.S. Food and Drug Administration approved the Pfizer COVID-19 vaccine for use in children 12 to 15 years old on Monday.

The FDA had previously approved the vaccine for those 16 and older.

“The FDA’s expansion of the emergency use authorization for the Pfizer-BioNTech COVID-19 Vaccine to include adolescents 12 through 15 years of age is a significant step in the fight against the COVID-19 pandemic,” said Acting FDA Commissioner Janet Woodcock, M.D. “Today’s action allows for a younger population to be protected from COVID-19, bringing us closer to returning to a sense of normalcy and to ending the pandemic. Parents and guardians can rest assured that the agency undertook a rigorous and thorough review of all available data, as we have with all of our COVID-19 vaccine emergency use authorizations.”

Pfizer in late March released preliminary results from a vaccine study of 2,260 U.S. volunteers ages 12 to 15, showing there were no cases of COVID-19 among fully vaccinated adolescents compared with 18 among those given dummy shots.

Kids had side effects similar to young adults, the company said. The main side effects are pain, fever, chills and fatigue, particularly after the second dose. The study will continue to track participants for two years for more information about long-term protection and safety.

Pfizer isn’t the only company seeking to lower the age limit for its vaccine. Results also are expected by the middle of this year from a U.S. study of Moderna’s vaccine in 12- to 17-year-olds.

But in a sign that the findings were promising, the FDA already allowed both companies to begin U.S. studies in children 11 and younger, working their way to as young as 6 months old.

More than 131 million doses of Pfizer’s vaccine have already been administered in the U.S., where demand for vaccines among adults has dramatically slowed in recent weeks.

While younger people are at dramatically lower risk of serious side effects from COVID-19, they have made up a larger share of new virus cases as a majority of U.S. adults have been at least partially vaccinated and as higher-risk activities like indoor dining and contact sports have resumed in most of the country. Officials hope that extending vaccinations to teens will further accelerate the nation’s reduced virus caseload and allow schools to reopen with minimal disruptions this fall.

The U.S. has ordered at least 300 million doses of the Pfizer shot by the end of July, enough to protect 150 million people.

The Associated Press contributed to this report.