Updated at 3:30 p.m.

The first COVID-19 vaccines given in Massachusetts will go to medical workers on the front lines of the epidemic beginning this month, with first responders and residents of elder care homes, homeless shelters and prisons also near the front of the line.

Gov. Charlie Baker laid out details of his three-phase plan to distribute the vaccines when they become available at his daily coronavirus press conference Wednesday at the State House. After all three phases of the plan are complete, Baker hopes the majority of the state's population will have access to the vaccine by April.

"Both the Moderna and Pfizer vaccines take about six weeks to provide a person with immunity from the virus," Baker said. "That means that while the first doses will be administered shortly, we're several months away from safely vaccinating a majority of the people of Massachusetts."

Phase one of the vaccine plan calls for clinical and non-clinical health care workers on the front lines of COVID care to receive shots first, then residents of long-term care and rest facilities, first responders, residents of correctional facilities and homeless shelters, home-based health care workers and those providing non-COVID-19 care.

The state's first order is forl 60,000 doses. Phase one is expected to require 300,000 doses.

Health and Human Services Secretary Marylou Sudders said she was thrilled by the recommendation of Baker's COVID advisory group to include prisons and homeless shelters among other congregate care settings, like elder care facilities, where residents are particularly vulnerable.

"From an equity perspective, where people are together and at risk in the same situation, we felt it was really important to prioritize that group," said Dr. Paul Biddinger, the chair of the advisory group and director of the Center for Disaster Medicine at Massachusetts General Hospital.

Inoculating prisoners before some other portions of the population sparked a degree of outrage in Colorado, where Gov. Jared Polis took issue with the recommendations of his own vaccination task force.

One fear, as The Colorado Sun reported at the time, is that an outbreak in a prison, where there is little ability to social distance, could spark a wider outbreak in the community at large.

The second phase of the Massachusetts rollout plan, estimated to come in February, will include people at the highest risk of complications from COVID-19, along with teachers, transit workers, grocery store employees and public health workers. Later in phase two, which is estimated to run through April, vaccinations will include those over 65 and those with lower but still significant risk of complications.

Nearly 2 million doses of the vaccine will be included in the second phase.

Boston Public School Superintendent Brenda Cassellius welcomed the news that pre-k and k-12 teachers and staff will be part of the second phase of vaccinations while appearing on GBH News' Boston Public Radio on Wednesday.

Phase three, when the general public will receive vaccination, will start in April, according to Baker's plan. By then, the state hopes enough vaccine will be manufactured to supply the rest of the state's over-18 population — around 5.8 million people.

"It's still too early, and there are too many variables that are still being worked out, to say exactly when this stage of the process would get underway. But our estimate is that this segment of the population could start getting vaccinated sometime in the spring," Baker said.

Baker is prioritizing communities of color in the phase-three distribution timeline and said he'll be focusing intently on reaching that population and making clear that vaccines are safe and effective.

"Communities of color and at-risk populations will be prioritized throughout this process in order to preserve life and prevent serious complications from COVID-related illnesses," the Rev. Liz Walker, senior pastor at Roxbury Presbyterian Church, said at the news conference.

Walker admitted that some Black and Latino communities may be initially distrustful of the vaccine's effectiveness.

"I think there's a lot of skepticism still," Walker said. "It's going to take a lot of work."