The US just authorized Pfizer-BioNTech's coronavirus vaccine for teenagers, making it the first COVID-19 shot OK'd for 12- to 15-year-olds

• US regulators have OK'd Pfizer-BioNTech's coronavirus vaccine for use in younger teenagers.
• The two-dose shot is the first vaccine to be authorized for use in the 12- to 15-year-old age group.
• US health officials have said they will soon be ready to start giving the shot to kids.

Teenagers in the US are now eligible for a leading coronavirus vaccine, as the Food and Drug Administration on Monday expanded the authorization for Pfizer-BioNTech's COVID-19 shot to include 12- to 15-year-olds.

The two-dose vaccine was approved in December for anyone 16 years old and up. US health officials said they were prepared to soon start giving the shot to younger teenagers.

Canada is the only other country to have OK'd a COVID-19 vaccine for younger teenagers. On May 5, it authorized Pfizer's vaccine for use among people 12 and older.

Expanding eligibility to include the younger age group could give the immunization campaign a boost. The US has seen the daily rate of people getting their first dose plummet since early April, from a peak of 1.9 million people a day to about 830,000 a day, according to data from the Centers for Disease Control and Prevention.

A major driver for that decline has been that a majority of adults in the US have already received at least one dose. About 58% of US adults have received at least the first dose of a vaccine, according to CDC data.

"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," Dr. Janet Woodcock, the acting commissioner of the FDA, said in a statement. "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 tested the vaccine in a clinical study that enrolled 2,260 children ages 12 to 15. Half of the volunteers received Pfizer's shot, while the other half got a placebo injection. Overall, the trial recorded 18 COVID-19 cases, all in the placebo group. Side effects of the shot were in line with those observed in people 16 to 25 years old, Pfizer said.

Pfizer and other vaccine developers are also testing COVID-19 shots in younger populations down to 6-month-olds

The New York drugmaking giant is still testing the shot in younger ages, hoping to further expand its eligibility later this year.

In September, Pfizer anticipates study results showing whether the shot works in children ages 2 to 11.

The final step down for kids - from 6-month-old babies to 2-year-olds - should produce data in November, according to Pfizer's projections.

Other leading vaccine developers are also testing their shots in younger populations.

On May 6, Moderna said its vaccine was highly effective in an initial review of a clinical trial enrolling more than 3,000 teenagers. The Massachusetts biotech said it was "in discussions with regulators about a potential amendment to its regulatory filings" after those early results. Moderna is also enrolling volunteers for a study testing the vaccine in kids 11 years old all the way down to 6 months old.

Johnson & Johnson also started testing in April its single-dose vaccine in adolescents 12 to 17 years of age.