More than half of people in Massachusetts have now received at least one dose of a COVID-19 vaccine. But there are signs the pace of vaccination may be slowing, possibly because younger people who are now eligible don’t feel the same sense of urgency as older residents, who are more vulnerable to the virus.

“We are starting to see a change in the pace of booking our vaccine appointments, so our experience is directionally similar to the other [states], but not necessarily to the same degree,” said Dr. Paul Biddinger, medical director for emergency preparedness at Massachusetts General Brigham and chair of the state's COVID-19 Vaccine Advisory Group.

The state’s weekly vaccine report out Thursday said that 53% of residents have gotten a shot so far, with just under 6 million shots administered — about 84% of the doses that have been shipped to the state. At the same time, some vaccination sites are already beginning to see noticeably fewer people coming in the door.

“I think this is starting to indicate that we will need to keep working hard to make sure the whole population understands why we need everyone to get vaccinated, to make vaccinations as accessible as possible so those with barriers are able to get vaccinated easily and to reach out and answer people’s questions and concerns that might make them hesitant,” Biddinger said in an email.

Since Monday, UMass Memorial Health Center’s vaccine clinic on Front Street in Worcester has seen fewer than 500 people a day, according Candra Szymanski, the site’s clinical supervisor. It has the ability to vaccinate 600 people a day and has regularly distributed up to 570 of those shots. But "something changed dramatically this week,” Szymanski said.

The UMass Memorial site is focused on vaccinating its own patients first, and then any extra available appointments are opened up to others through the state’s registration website. But that wasn’t enough to fill up the available spots this week, and Szymanski said she tried to recruit some more people from the neighborhood.

“I hung a sign saying, ‘Walk-ins: Vaccines available,’ and I put it in a restaurant next door,” she said.

“I'm just hopeful it's not a trend,” she said.

In New Bedford, a vaccination site run by FEMA could be closed soon if more people don't show up to get shots there.

“The times that I've been down there, the place has been near empty,” said Kevin Gallagher, the fire chief in neighboring Acushnet, who made a plea on Facebook this week to encourage more people to show up to the site, which doesn’t require an appointment.

Gallagher said FEMA is now only committing to giving first shots through next week because of the low turnout.

“They kind of have a fiduciary responsibility to say, ‘OK, this isn't working here. Where do we want to take our assets for a better return on investment?’” Gallagher said. “What we're trying to say is, ‘Give us a little time to promote this.’”

Gallagher said he’s optimistic their efforts to publicize the site, including automated calls to the community, will pay off with a good turnout at the site, which is open from Saturday through Tuesday.

“We don't want to lose this opportunity until our numbers, which are hovering in the mid 40% of people vaccinated, are in the 60 to 70% [range],” he said. “You know, maybe it's a pipe dream, but we hope that the federal government will give us a little bit longer to take advantage of this opportunity.”

Some of the hardest people to reach in and around New Bedford are immigrants who may not be in the country legally, Gallagher said, and who may be unwilling to go to a FEMA vaccination site.

“There's a hesitation by those folks to go to a facility that looks like the heavy hand of the U.S. government, because of immigration concerns,” he said.

A spokesperson for FEMA did not respond to an inquiry from GBH News.

The Baker administration announced $8.8 million in grants and contracts for community organizations on Thursday in an effort to increase awareness and access to the COVID-19 vaccine in the 20 cities and towns hardest hit by the pandemic, including New Bedford.

At the state’s mass vaccination sites, the demand for vaccines has not yet fallen behind supply, Rodrigo Martinez, chief marketing and experience officer at CIC Health, which is administering those sites, said in a written statement sent to GBH News.

“We all know and expect this may start shifting in the coming weeks to supply being larger than demand, so CIC Health and the state are doing everything they can to continue communicating the importance of vaccinations, both across the mass vaccination sites and the pop up sites we are supporting,” Martinez said.

“Definitely the rush is over,” said Dr. Marcia Testa, president of the Massachusetts Association of Health Boards. “The demand is not over, I don't think.”

Massachusetts has been successful at vaccinating its older residents, with nearly 87% of people over the age of 65 getting at least one shot, according to Thursday’s report. That’s compared to about 46% of Massachusetts residents in their 20s who are vaccinated so far.

“Now we've gone into the point where the people who rushed to get vaccinated, and all the people that booked up early on and then had to get their second shots — we’re coming to the tail of that, I think,” Testa said. “And then now you'll get the people coming on board in sort of the second wave.”

Testa said those younger residents likely don’t feel the same sense of urgency to get vaccinated as older people did. But that doesn’t mean they’re not going to get vaccinated.

“They’re just, I think, going to take their time,” she said.