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CNN  — 

The US Food and Drug Administration expanded the emergency use authorization for Pfizer’s Covid-19 vaccine on Monday to include people ages 12 to 15.

This is the first Covid-19 vaccine in the United States authorized for use in younger teens and adolescents; the vaccine had previously been authorized for people age 16 and older. Covid-19 vaccines from Moderna and Johnson & Johnson are authorized for use in people age 18 and older.

To support the extended use, the FDA reviewed data submitted by Pfizer. The company said at the end of March that a clinical trial involving 2,260 12-to-15-year-olds showed the vaccine’s efficacy is 100% and it is well tolerated.

“It was a relatively straightforward decision,” Dr. Peter Marks, Director of FDA’s Center for Biologics Evaluation and Research, the arm of the FDA that regulates vaccines, told reporters Monday evening.

The FDA looked at the Pfizer safety and efficacy data. The agency also looked at the immune responses of some of the children who were vaccinated, and compared them to the immune responses of older teens and adults who got the shot.

“The response to the vaccine was excellent and in fact it was even better, really, in the younger age group than it was in the 16-25 age group,” Marks said.

“The safety profile was very similar in 12-15-year-olds as in 16-25-year-olds.”