Massachusetts will shut down four of its seven mass vaccination sites, including the facilities at Gillette Stadium and the Hynes Convention Center, as the state transitions its COVID-19 vaccine strategy toward mobile sites with a greater emphasis on populations still hesitant to get the shots.

Gov. Charlie Baker announced Monday that the Gillette, Hynes, Natick and Danvers sites will close by the end of June.

"At this point, we're adjusting our vaccine distribution strategy to be more targeted, and we'll shift vaccines to smaller scale operations that can focus on particular communities or particular populations," Baker said.

According to Baker, the state will shift its allotment of vaccines to places like community health centers and local boards of health to reach out to individuals who haven't taken advantage of the larger sites.

"You may not be comfortable going to a mass vax site, but if you got a call from your doctor, you might go get your shot," Health and Human Services Secretary Marylou Sudders explained.

The change to the vaccination program comes as Massachusetts approaches nearly four million vaccinated residents, nearly 58% of the population, and as cases, hospitalizations and death count have all dropped significantly.

"Everything's pointed in the right direction," Massachusetts General Hospital Center for Disaster Medicine director Dr. Paul Biddinger said at the press conference.

"So we're really, really making great progress. I think the most important thing, again, to suppress variants, to make sure we stay healthy, is to finish the work that we've been doing so far," Biddinger said.

Baker said the state will begin to consider how to vaccinate children between the ages 12 to 15 once the Food and Drug Administration and other federal authorities authorize the vaccines for use in people younger than 16. When that happens, Baker said, he would consider making vaccination required for students returning to school in the fall.

Asked if his decision to not require state employees to get vaccinated contradicts his goal to get as many people as possible innoculated, Baker said he prefers an incentive-based voluntary program.

Baker added that many of the people still hesitant about getting the vaccine have valid reasons and he would not "play that game" when it comes to firing an employee for refusing to be vaccinated.

"The idea that we would take those folks and basically make them choose between their rent and their food on the table and all the rest, when they have in some cases very legitimate reasons to be nervous about a government-run program that's going to put a shot in their arm, no, I'm not going there. I'm not going there," Baker said.