As pressure mounts for a new statewide mask mandate, experts are divided on whether such requirements work

Masks are required indoors in public places in Chelsea.Pat Greenhouse/Globe Staff

Amid growing calls for a statewide mask mandate to blunt surging COVID-19 cases and rising hospitalizations, more communities are starting to take action.

Several, including Georgetown, Lowell, Chelsea, and Salem, have in the past two weeks reimposed mask rules for indoor public spaces.

And on Tuesday, the state’s leading medical group, the Massachusetts Medical Society, added its voice, calling for a statewide requirement for masks in indoor public spaces.

“As the number of COVID-19 cases and hospitalizations continue an alarming upward trend that is straining our health care system, the physicians of the Massachusetts Medical Society recommend that masks be required at all public indoor settings in the Commonwealth, regardless of vaccination status,” said Dr. Carole Allen, president of the society, in a statement.

But Governor Charlie Baker has resisted those calls, reiterating on Monday that he had no plans for a statewide mask mandate, noting that 5 million residents in Massachusetts are fully vaccinated and 1.5 million of those have booster shots.

New data from the Metropolitan Area Planning Council shows that among the 101 communities it tracks in Greater Boston, nearly half now have some form of indoor masking rules. At least 22, including Boston, require masks in all indoor public spaces, and another 24 have mandates for at least their municipal buildings.

Some infectious disease experts say mandates alone may not be enough to convince a pandemic-weary public to don face coverings once again. John Brownstein, an epidemiologist at Harvard Medical School and chief innovation officer at Boston Children’s Hospital, concluded in a study published earlier this year that communities with high reported rates of mask wearing and physical distancing were able to better tamp down transmission of the virus — but government mandates did not seem to boost the number of people wearing masks.

“The mandate itself is not necessarily the most effective,” Brownstein said. “What we have found, generally speaking, is that [mask wearing] goes up when there is a threat other than a government mandate.”

He said a surging number of cases and rising hospitalizations post-Thanksgiving, coupled with so many unknowns about the rapidly spreading Omicron variant, are just as likely to convince people to put their masks back on.

And the latest data from Carnegie Mellon University’s COVID-19 Trends and Impact Survey appears to agree with that assessment. It shows that the percentage of Massachusetts residents who report wearing a mask climbed to 67 percent earlier this week, from 61 percent just before Thanksgiving.

Ali H. Mokdad, professor of health metrics sciences at the University of Washington’s Institute for Health Metrics and Evaluation, said there is no doubt that masks “can control the spread of this virus.”

The institute projects that if 95 percent of Massachusetts residents wore a mask,, by March 2022 COVID-19 mortality would drop to just three new deaths per day, instead of the 29 per day predicted if nothing changes. That would prevent roughly 1,500 deaths.

On Monday, the state Department of Public Health reported a seven-day average of 17.4 deaths.

But Mokdad cautioned that the IHME model is three weeks old and doesn’t yet take Omicron into account. Once the fast-spreading new variant is added into calculations, the effects of masking would be much greater, he said.

Mokdad supports vaccines and vaccine mandates as the first line of defense, but he cautions that vaccinated people could play a big role in spreading the virus if they go out without masks. Vaccinated people may face little risk of becoming severely ill, but they can still get infected and spread the virus to vulnerable or unvaccinated people without knowing it.

“Mask mandates do work,” Mokdad said.

But Joseph Allen, director of the Healthy Buildings program at Harvard T.H. Chan School of Public Health, said a mask mandate would not be the most useful tool at this point.

For people who are fully vaccinated and boosted, masks provide “little additional benefit,” Allen said at an online press briefing Tuesday. And those who would most benefit from wearing masks — unvaccinated people — are the least likely to wear them.

Allen said public health officials should have eased up on the mask messaging during last spring and summer when the public knew that disease transmission was low. Now, “fatigue has set in.”

“We’ve taken the power of this tool out of our arsenal by failing to roll it back at the appropriate time, so that we could put it back in place at an appropriate time,” he said. “The public is largely frustrated by that messaging — when they knew it was low risk at certain times, yet the public health messaging stayed on code red.”

Instead, public policy should focus on vaccinations, boosters, and testing, he said.

Allen favors the approach New York City has taken, requiring either vaccination or a negative test to enter a public venue. “In a fully vaccinated environment I don’t think people need to be wearing a mask,” he said.

In some smaller Massachusetts cities and towns, mask mandates may have become impractical for health departments already stretched thin.

Public health officials in Leominster and Gardner, for example, have opted against a mask requirement, saying Tuesday that because of their efforts to run vaccine and testing clinics, they have no staff members left to dedicate to enforcing mask practices.

“A mask mandate requires follow-up and enforcement and generates complaints when people aren’t complying with it, and that will thin [our] staff out to a point where they may not be effective at any one thing,” said Jeffrey Stephens, Leominster’s health director. “So our department has decided to focus on mitigation through testing and vaccines.”

Stephens, who manages a staff of six in a city of 40,000, said a majority of residentshave begun wearing masks with the recent spike in cases. Instead of a mandate, he said, they’ll hope to increase mask compliance with educational messaging.

Meanwhile, in Boston, which reimposed its indoor mandate in September, a stroll through neighborhoods Tuesday revealed fairly high adherence to the rules.

Inside Dorchester’s Price Rite grocery store, all shoppers and store employees wore masks. Next door, at Target, all faces also remained covered.

Outside, in the parking lot, some people even kept their masks on as they unloaded their shopping carts into their cars.

But just a view miles away, in Milton, which requires masks only in town buildings, few face coverings could be seen in local stores.

An older couple held hands as they walked into a wine shop, maskless. At Mackie’s Barber shop, several hairdressers and customers were lounging around the salon, their smiles and laughter evident without masks.

At the Coffee Break cafe, the only mask in sight was the one resting on a customer’s chin as she drank her beverage. Two baristas behind the counter were both maskless as they prepared drinks for guests.

One of the baristas, Jeremy Lewison, 19, of Milton, pulled a mask from his pocket and said he typically puts it on when the store gets crowded. But with only a few customers inside the cafe, he didn’t feel like he needed it.

“At this point, I’m trusting everyone to make their own decisions, but if there’s a mandate and people continue not to wear masks that’s a whole different story,” Lewison said.

But Daniel Vasquez, 38, was walking nearby with a mask firmly in place. Vasquez, of Roslindale, was in Milton visiting his mother. He said he wears masks regardless of whether there’s a mandate.

“For me it’s really an easy decision,” he said, adding that his wife is asthmatic.

Vasquez said it’s frustrating when he sees people without masks in the grocery store and around town.

“It’s a disregard for others that bothers me. It’s not only for yourself, you’re protecting others and participating in something to keep people safe,” he said. “I would prefer a mandate.”

Travis Andersen and Andrew Brinker contributed to this story.