BOSTON (SHNS) – All teenagers and pre-teens ages 12 to 15 who pre-registered through the state’s online portal for a COVID-19 vaccine will be contacted Thursday morning with the chance to book an appointment after the Centers for Disease Control on Wednesday evening gave the green light for use of the Pfizer vaccine in younger Americans.

The Baker administration’s COVID-19 Command Center said newly eligible young people will be able to book an appointment at any of the 900 vaccination locations that has Pfizer doses. The administration has also begun reaching out to primary care and pediatric providers to encourage them to order and administer Pfizer vaccines to eligible patients through their practices.

While the administration did not say how many 12-, 13-, 14- and 15-year-olds pre-registered for a vaccine while they waited for federal approval, the state estimates that there are roughly 400,000 residents living in Massachusetts in that age bracket. The Pfizer vaccine was previously being distributed to anyone 16 or older, while the Moderna vaccine has only been approved for use in individuals at least 18 years old. A CDC advisory panel on Wednesday endorsed the use of the Pfizer vaccine in younger populations as both safe and effective, and its recommendation was accepted by CDC Director Rochelle Walensky.

CIC Health, which operates the vaccine clinics at the Hynes Convention Center, the Reggie Lewis Center and pop-up sites, said 12- to 15-year-olds would be welcome beginning Thursday to schedule an appointment or walk in. Consent forms signed by a parent or legal guardian are required by CIC for all patients under 18.

“The FDA and CDC approval of Pfizer’s COVID-19 vaccine for adolescents ages 12 to 15 is an exciting development in our battle against the COVID-19 pandemic. CIC Health is humbled to be part of Massachusetts’ success in leading the nation in vaccination and we stand ready to welcome this new eligibility group to our sites,” the company said.

Massachusetts has fully vaccinated more than 3 million residents so far, and Baker has said the state is on track to meet its initial goal of 4.1 million adults by early June. The approval of a vaccine for a younger subset of the population, however, opens up the possibility to vaccinate an even greater portion of Bay State residents.