TD Garden will up mask enforcement. But will that be enough to keep fans in the stands amid Omicron?

Getting fans to keep on their masks is a top priority and big challenge at TD Garden.Jim Davis/Globe Staff

TD Garden is stepping up enforcement measures to remind its 18,000 or so Celtics and Bruins fans that they need to do a better job of keeping their masks on.

That may not be enough to keep Boston’s biggest indoor arena, as well as sports arenas around the country, open to full capacity this coming winter.

With the highly transmissible Omicron COVID-19 variant expected to sweep through the country in the coming weeks and place increasing pressure on already understaffed hospitals, a leading public health expert sees public officials having little choice but to reduce capacity by early next year.

“If our hospitals are pressed even more and if there are double the number of cases per day in six weeks, I think it will be untenable to keep a fully packed arena with people munching on popcorn,” said Dr. Asaf Bitton, executive director of Ariadne Labs, the health systems innovation center at Brigham and Women’s Hospital and the Harvard T.H. Chan School of Public Health.

Cognizant that “in these COVID times people who make predictions are more often wrong than right,” Bitton said “it’s important to try to forecast and I would say it’s hard to see that there aren’t at least some reductions in density” at indoor arenas.

Bitton recommends getting in front of the Omicron arrival with layers of defense.

For example, the Garden’s trying to increase mask-wearing by walking through the aisles and concourses with extra masks and “Mask Up” signs and flashing reminders upon arrival and repeatedly during the games on video boards.

Will there be a return to limited seating for games at TD Garden like we saw last spring?Elise Amendola/Associated Press

They could go further, said Bitton.

Because cloth masks offer the lowest level of personal protection, arenas could require patrons to at least wear surgical masks that the arena would provide.

But keeping those masks on is a challenge because of the escape clause that patrons can slide it down while they’re eating or drinking.

“The last two weeks with the numbers going up, we’ve been watching as closely as everyone else,” said TD Garden spokesperson Tricia McCorkle. “People are good about wearing their masks when they’re going in,” but it’s when fans are in their seats, when they’re eating or, frequently, not eating, or getting up to go to the bathroom when they forget.

“We know the enforcement is not perfect — it’s just tough, and you see it in society at large, it’s not just at TD Garden.”

In a statement, Amy Latimer, president of TD Garden and also a member of the newly formed COVID-19 Advisory Committee assembled by Mayor Michelle Wu, acknowledged that wearing masks is more important than ever and that the arena also requires proof of vaccination or a negative test from all guests.

“While the arena experience presents unique challenges, the team at TD Garden has been diligent about reinforcing the necessity of masks to maintain the safest environment possible,” said Latimer. “We continue to monitor and adapt and we thank the fans who have been doing their part to help us keep live events live.”

TD Garden will take its cue from the City of Boston when it comes to any decision to revert to crowd capacity restrictions that were in place over last winter and into this spring and summer.

Asked if the city has discussed reducing capacity or banning all fans, a city spokesperson replied in an email, “While we work to get every Bostonian vaccinated, the city will continue to track the latest COVID-19 data and trends, and make decisions based on science. We urge all Bostonians to get vaccinated and boosted, and to continue to follow the indoor mask mandate to keep ourselves and others healthy.”

The look of TD Garden changed last season when fans were allowed back on a limited basis.Charles Krupa

The imminent arrival of Omicron means the public and private sectors might have to return to a playbook they thought they were done with.

“I’d recommend to take a look now at some options that might seem inconvenient and unpalatable,” said Bitton. “I think in some locations, and it’s sort of hard to predict exactly where, the transmissibility of Omicron will put a lot of pressure on public health officials and state and local leaders to do something by the end of January, into February and that something may initially start with really decreasing large public indoor gatherings.”

There’s always the chance that officials would not have to make an unpopular decision like reducing capacity at an arena simply because a rise in the number of college and professional athletes sidelined by positive tests will make fielding a team impossible and leading to even more postponed games than are already occurring in the NBA and NHL.

Bitton said he’d be “shocked” if a number of teams who play and practice indoors will not be taken offline for two weeks or more “because it’s going to spread in those tight settings very predictably — it’s just physics and biology.”

In the case of the NFL’s New England Patriots, who play in the open-air Gillette Stadium, Bitton is more optimistic.

“Gillette is just wide open, it’s a windy stadium, and those are all really good things from the point of view of reducing airborne transmission,” said Bitton.

Demanding full vaccination from patrons may not meet the threat represented by Omicron. While initial data suggests that boosted individuals are fending it off for the most part, Bitton pointed out that in addition to the unvaccinated, the variant is being transmitted among the vaccinated who have yet to receive their booster shots.

“Are we ready for that, are arenas ready to say you can only enter an arena if you’ve been boosted?” said Bitton. “That’s only about 25, 30 percent of people. That’s probably a tough sell.”

While Bitton sees a harsh impact from Omicron’s arrival, “I don’t think that we need to have a public freak out about Omicron. But I think that we need to take it with the seriousness of purpose and action that is required. And I think one of the first areas we have to consider are huge public gatherings — I’m not talking about 100 people at your church or synagogue, I’m talking about a huge public gathering of 18,000 to 24,000 people, however big the indoor arenas are.”

That said, Bitton offered a closing note that could offer a small measure of optimism.

“It’s hard to see that there might not be at least some partial indoor shutdowns for a little while but America has shown its interest in keeping life as we know it and understand it going,” said Bitton. “So, I think that the shutdowns are going to be the exception and not the norm — that would be my prediction, with deep humility.”