BOSTON (CBS/AP) – The CDC endorsed use of Pfizer’s COVID-19 vaccine in kids as young as 12 Wednesday.

Earlier in the week, the Food and Drug Administration cleared the expanded use of Pfizer’s shots, citing evidence the shots worked as well in those 12 to 15 years old as those 16 and older.

Nearly 17 million children across the country will become eligible immediately.

Pfizer says the vaccine is 100-percent effective in 12-to 15-year-olds, which is higher than for adults.

The FDA approved it for emergency use Monday, but most states decided to wait until the CDC voted to formally recommend use of the vaccine.

Governor Charlie Baker said Wednesday that Massachusetts is ready to roll out the shot to this new age group and families can register for a vaccination at mass.gov/covid-19-vaccine.

Gov. Baker also said he expects kids to be able to get the vaccine at their pediatrician’s office and at community clinics.

Anyone who pre-registered in Massachusetts will be contacted Thursday morning to schedule an appointment at any of the 900 locations in the state that offers the Pfizer vaccine.

CVS announced that vaccine appointments for the new age group are now available for scheduling at more than 5,600 CVS Pharmacy locations nationwide.

Boston Children’s Hospital began vaccinating kids 12-to-15 years old on Tuesday.

“Getting the vaccine into 12-to-15 year olds will further help increase immunity among the population, gets us a step closer to herd immunity so there will be both direct and indirect benefits,” Dr. Ofer Levy, the Director of the Precision Vaccines Program at Boston Children’s, told WBZ-TV.

The American Academy of Pediatrics found nearly 25-percent of all new COVID cases are in kids and teens.

WBZ-TV’s Dr. Mallika Marshall said parents should be aware of the timing of getting their kids vaccinated for the summer.

“That’s because, from the time your child gets the first dose, it will take 5 weeks to build full immunity. They will get their first shot, their second three weeks later, and two weeks after that they’ll be considered fully vaccinated. I think many parents would like their children to have even more freedom at summer camps and for summer travel so I suggest you try to get your kids vaccinated sooner rather than later,” she said Wednesday.

“And parents, please call your pediatrician with any questions or concerns. We know parents are more likely to listen to the advice of their personal physicians than that of personalities or politicians.”

(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)