Provincetown officials during an emergency meeting late Sunday afternoon approved a new indoor mask mandate and a measure clearing the way for stricter capacity limits on local businesses amid a surge of new COVID-19 cases since the July Fourth holiday weekend.
The measures came as the country battles increasing numbers of infections fueled largely by the virus’s Delta variant and a lagging national vaccination effort.
“COVID, unfortunately — and I think it’s depressing for many of us — isn’t going away anytime soon,” said Provincetown’s town manager, Alex Morse, during the meeting. “Provincetown is experiencing what other places will be experiencing, earlier.”
Provincetown issued an indoor mask-wearing advisory early last week after reporting what health officials are calling a cluster, which has grown to include 551 cases as of Friday, including some caused by the more infectious Delta variant, Barnstable County officials said during Sunday’s meeting.
Nearly 70 percent of those cases occurred among vaccinated people. Three hospitalizations have been linked to the cluster, they said.
Local public health experts said in interviews earlier Sunday that recommendations that people wear masks — even if they are vaccinated — may be a necessary step to help stop the virus’s spread, along with limiting the number of people gathering indoors in places like restaurants or stores.
Those measures are all the more important in a place like Provincetown, a vacation spot that draws tourists from areas where the number of vaccinations are lower than in Massachusetts.
Dr. Robert Horsburgh, a Boston University professor of epidemiology, said Sunday in a phone interview that any community whose economy is based on tourism should be working on further ways to stop the spread of COVID-19.
“We need to be more careful than we did before.... We do need to be cognizant that the virus is getting ahead of us. It’s unfortunate. Had the country gotten everyone vaccinated, we wouldn’t be seeing a new variant,” Horsburgh said.
“I would love COVID to be over, but it’s not,” Horsburgh said.
In Massachusetts, more than 60 percent of its roughly 7 million residents have been fully vaccinated, according to state data. Across the United States, about 163 million people — about 49 percent of the country’s population — are vaccinated, according to the US Centers for Disease Control.
The Provincetown mandate comes during the height of the summer tourist season, when the Cape Cod community typically attracts tens of thousands of visitors and after Governor Charlie Baker lifted most of the state’s pandemic health restrictions in May.
On Thursday, Baker said he had no plans to reinstate statewide COVID-19 restrictions. Communities should be able to pursue strategies, he said, “that are more effective and appropriate to them.”
The CDC estimated that about 83 percent of the nation’s cases from July 3 to July 17 are attributable to the Delta variant. In New England during that period, more than two-thirds of cases were due to the Delta variant, according to the Massachusetts health department.
Dr. David Hamer, a physician at Boston Medical Center and a Boston University epidemiologist, said Sunday he is concerned that the Provincetown cluster is one of multiple impending outbreaks elsewhere in the state.
State data tracking new cases, positivity rates, and presence of virus in wastewater is indicating more transmission, he said, much of it driven by the Delta variant. And in areas that attract a lot of visitors from out of state, like Provincetown, the risk for movement of the virus across state lines is substantial, Hamer said.
Control measures to limit the virus — like getting more people vaccinated — are going to need to be intensified.
“The Delta variant and its characteristics is providing a new challenge,” Hamer said. “And people need to maintain their guard. We’re not out of this yet.”
Health experts have said that the vaccines are extremely effective against COVID-19, including its Delta variant, and reduce the risk of severe sickness and death. But unvaccinated people remain at risk for contracting COVID-19, and officials have continually urged eligible people to get vaccinated.
Sean O’Brien, Barnstable County’s chief health officer, said at Sunday’s meeting that vaccinated people who got infected in the Provincetown cluster were largely asymptomatic or had mild symptoms.
“What we’re seeing here is just a very good example of how well the vaccine is working,” O’Brien said. “It’s really important to remember: People need to still be vaccinated.”
Dr. Anthony Fauci, the country’s top infectious disease expert, told CNN’s “State of the Union” news program that health officials are considering whether to recommend vaccinated people wear masks.
Dr. Ashish Jha, dean of the Brown University School of Public Health, said in a series of Twitter posts Sunday afternoon that the situation has “clearly turned worse” since June, when the numbers of infections were falling.
The Delta variant is more contagious than anything officials have seen before and the country “hit a wall” with under 50 percent of the population fully immunized, Jha said.
There are also signs of waning immunity, he said, with more breakthrough infections in vaccinated people.
Public health measures such as masks, reduced indoor gatherings, improved ventilation, and testing will help, he said, but much higher levels of population immunity are needed.
Last week, the Boston Public Health Commission reported that at least 35 Boston residents with cases had been traced back to the Provincetown cluster. The overwhelming majority of those cases occurred in people who were vaccinated, the commission said.
On Thursday, the commission asked Boston residents who had traveled to Provincetown since July 1 to get tested and self-isolate for at least five days and receive a negative COVID-19 test.
The meeting in Provincetown comes also after other nearby communities reported increasing numbers of new COVID-19 cases.
In Wellfleet, officials reported ‘‘about eight cases” of COVID-19 as of Sunday. Officials there asked people to wear masks indoors and practice social distancing.
And on July 17, Truro officials announced a growing caseload of residents who were positive for COVID-19, including many vaccinated people, following Fourth of July festivities. Earlier in the month, Truro’s Board of Health ordered masks in all public buildings.
Scott McGann, Falmouth’s health agent, reported in a Thursday briefing that the town has seen an uptick in cases this month. As of Thursday, 17 cases were reported in the town, up from three cases in June.
A mask advisory in place since late May asks people to wear masks in indoor public spaces.
“We haven’t gotten much from the state about doing anything [other] than staying the course we are on,” McGann said. “Delta is here. No doubt about it, so we’re going to keep monitoring it.”
Globe correspondent Alexandra Chaidez contributed to this report.