This Jan. 24, 2021, file photo shows a vial of the Pfizer vaccine for COVID-19 in Seattle. U.S. regulators on Monday, May 10, 2021, expanded use of Pfizer's shot to those as young as 12, sparking a race to protect middle and high school students before they head back to class in the fall. Credit: Ted S. Warren / AP

A handful of Maine providers are already scheduling appointments after Gov. Janet Mills said Tuesday that they could begin offering the Pfizer COVID-19 vaccine to children aged 12 and older.

But the availability of appointments is largely limited to sites run by major hospital systems, as the Pfizer vaccine requires ultra-cold storage and comes in packs of 975. The Moderna and Johnson & Johnson vaccines are not yet approved for people under the age of 18.

As of Monday, Northern Light Health was scheduling vaccination appointments for kids between the ages of 12 and 15 at three locations in Bangor, Presque Isle and Caribou. All patients under age 18 must have a parent or guardian register on their behalf and sign a consent form. Parents are required to accompany kids under age 16.

In southern Maine, Mid Coast Hospital in Brunswick is encouraging parents to make appointments for their eligible children, while walk-in vaccinations are available to people aged 16 and older. Intermed, the outpatient group in South Portland, is also allowing parents to make appointments for kids aged 12 and older. MaineHealth, which operates several sites, is currently allowing preregistrations for kids between the ages of 12 and 15.

Several hospitals have also begun to assist with school-based vaccination efforts. MaineHealth has clinics for 16- and 17-year-olds scheduled at Poland Regional High School on Tuesday and Oxford Hills Comprehensive High School on Thursday. Brewer High School began offering first doses of the Pfizer vaccine to 16- and 17-year olds on Monday, while Bangor has a clinic planned at Bangor High School for students aged 12 and older on Friday.