Should Mass. residents be worried about tourists from coronavirus hotspots importing more illness?

Robin Halicki with her sister Marcia Hammerstrand from the Chicago area looked over John Hancock stone in the Granary Burying Ground.David L. Ryan/Globe Staff

Massachusetts has done the hard work. Nearly everything was closed down for months. Residents have socially distanced and are (mostly) wearing masks. Now, the state’s closely watched rate of positive COVID-19 cases is the lowest it’s been in weeks, and many restaurants and services are making a comeback.

But so, too, is tourism. And with such a sharp rise in infection rates in many Southern and Western states, should Massachusetts residents worry about visitors from coronavirus hotspots importing more illness here?

The possibility of tourist-borne coronavirus contagion prompted the governors of New York, New Jersey, and Connecticut, a tri-state region once ravaged by the virus, to issue a travel advisory on Wednesday directing people arriving from states with high coronavirus rates to quarantine for 14 days. New York’s advisory promises fines of up to $10,000 for violators.

Massachusetts has had a 14-day quarantine advisory in place since late March for all travelers coming into the state, but it includes no such fines, rendering it relatively toothless.

Exactly how many out-of-state visitors Massachusetts may see in these unusual times is not clear. Last year, though, more than 18 million poured in, according to state data. And more than 1 million were from states now struggling with a rising number of infections — California and Florida.

Many of these out-of-staters typically head to the Boston and Cambridge area, with about 550,000 Floridians and 550,000 Californians sightseeing around the Hub, according to the latest numbers from the Greater Boston Convention & Visitors Bureau.

Hordes of Texans visited last year, too. The bureau’s numbers show about 350,000 trekking around Boston in 2019, the most recent annual count. Texas is battling a surging number of COVID-19 cases this week, with 11 percent of all tests coming back positive, according to the Johns Hopkins tracker.

Visitor quarantines may seem like a smart intervention to keep the virus from crossing state lines. Symptoms can take up to 14 days to appear after someone is infected, and research suggests people can transmit the virus even when they’re showing no signs of illness, said Dr. Nahid Bhadelia, an infectious diseases physician and medical director of the Special Pathogens Unit at Boston Medical Center.

But a quarantine strategy may not be a realistic approach to stopping further infections, she said, because it’s hard to monitor every car crossing the border, and the state can’t stop travelers flying in to airports, which are federal sites.

“After states have been going it on their own, we are now quickly realizing our state is tied to [other] states,” Bhadelia said. “What happens in Florida or Arizona is not independent. Our borders are so porous.”

Legal issues associated with attempting to block or impede travel may also prove an obstacle, said Wendy Parmet, a professor of law, public policy, and urban affairs at Northeastern University.

“Travel advisories are themselves deeply problematic,” she said. “The dilemma is showing up the disaster of what’s been happening: the fact that we don’t have a federal policy, and no consistency among the states.”

She allowed that the plight of Massachusetts this summer “may be an instance where there is some merit to [travel quarantines] because you have situations with people coming in from jurisdictions that are not doing social distancing, or widespread use of masks, and it’s a real problem.”

But some coronavirus travel advisories issued by states, in the absence of a coherent national strategy, have already run into legal challenges, including Maine’s earlier rule mandating a 14-day quarantine with no other option, Parmet said. The rule was eased before the lawsuit played out. Maine now waives the quarantine for visitors who receive a negative COVID-19 test within 72 hours prior to arrival.

Some states have issued rules targeting a tourist’s place of residence rather than a blanket rule applying to everyone coming in. But that approach raises the risk of running afoul of the Privileges and Immunities Clause of the Constitution, which prevents state governments from discriminating against out-of-state citizens, Parmet said.

“Texas earlier in the pandemic tried to put a quarantine on people from Louisiana and it doesn’t work,” Parmet said. “It’s a statement. But we can’t rely on these kinds of measures to keep us safe when we have a patchwork system around the country the way we do.”

Texas had set up checkpoints along its border with Louisiana to enforce the rules, but lifted them a month later.

Back in April, the shoe was on the other foot: Massachusetts persistently ranked near or in the top five states for deaths, per capita infections, and the rate of those who tested positive for the virus.

Today, Massachusetts is among a minority of states with significantly declining numbers.

New York Governor Andrew Cuomo cited a similar success story for his state, once the nation’s epicenter for the virus, in announcing the region’s new travel advisory.

“We have to make sure the virus doesn’t come in on a plane,” Cuomo said at a news conference Wednesday.

The new rules for New York, New Jersey, and Connecticut which took effect Thursday will apply to travelers from states with an infection rate of more than 10 per 100,000 people over a seven-day rolling average, or a 10 percent or higher positivity rate among those tested over a seven-day rolling average.

Asked whether Massachusetts might consider a similar action targeted at specific states, Governor Charlie Baker on Wednesday brushed off the suggestion.

“You can’t mandate it,” he told reporters. “I mean, it’s not constitutional.”