Massachusetts will allow adolescents 12 and up access to the Pfizer COVID-19 vaccine starting Thursday, Gov. Charlie Baker announced Wednesday.

"Pending the CDC approval for this group, people aged 12 to 15 will be able to book appointments or access a walk-up appointment beginning on Thursday, May 13," Baker said.

The Centers for Disease Control and Prevention are expected to give the final OK for the vaccine's use in older children later Wednesday. Massachusetts is home to around 400,000 people in the 12 to 15 age group. Baker said the state has already contacted pediatricians about how best to administer the vaccine to their patients.

Baker also announced a program for employers to book blocks of vaccination appointments for workers at the state's mass vaccination sites and to provide mobile clinics that vaccinate employees on-site.

"The program is intended to provide two great options for employers of all sizes and is another way we're working to build out vaccine administration to get more people dosed safely and conveniently," Baker said.

The Republican governor was asked about a letter signed by over 100 Republicans vowing that they will leave the GOP if the party doesn't do more to embrace truth and disavow the influence of former President Donald Trump. Baker, one of the most prominent Republicans in the nation who opposed Trump before and throughout his presidency, said he was not approached to sign on to the letter.

"I've had my differences, as everybody knows, with plenty of folks in the party over the course of the time that I've been in public life," Baker said. "But I'm a big believer in what the party fundamentally stands for, based on what I believe it stands for."

Baker also told reporters at the press conference that he is monitoring, but not yet worried about, the ransomware attack on the Colonial Pipeline and a potential gas shortage affecting Massachusetts.

"At this point in time, it's not an issue in the Northeast, and that's primarily because a lot of our distribution comes from other sources," Baker said. "But we're paying a lot of attention to it."