To Todd Eckstein, Provincetown, Mass., seemed like the safest possible place to party for Fourth of July weekend. The Cape Cod vacation destination boasted not a single coronavirus case in June - and most importantly, a vaccination rate so high that people joked it had passed 100 percent. Immunization cards were checked at the waterfront hotel where people converged every evening for the town's famous "Tea Dance."

With rain pouring down, Eckstein recalled, people left the venue's pool and sun deck to squeeze inside "to the point you could hardly move." Masks were a thing of the past as a town of about 3,000 swelled to more than 60,000 and the main drag buzzed like a carnival.

Fully vaccinated but feverish after getting back to Ohio, Eckstein took a rapid coronavirus test - it was positive. A fluke? he thought. But the next day he tried sniffing the most pungent foods he could find: Mustard, horseradish, Buffalo Wild Wings powder. Nothing. Soon, he was googling "Provincetown covid" every day for information.

"I just was shocked," he said.

July festivities at the tip of Cape Cod stress-tested the vaccines against indoor crowds and the fast-spreading, game-changing delta variant of the coronavirus. Provincetown's outbreak of overwhelmingly mild or no-symptom cases would grow to more than 1,000 people, about three-fourths of them vaccinated - a phenomenon that led experts to believe the immunized can in rare cases spread COVID-19. The findings helped spur new national masking guidance and left Provincetown's leaders, locals and infected visitors grappling with the same questions facing the country: What should life look like under delta? Can people still have the let-loose summer they waited for?

"Does this mean after every holiday that ... we as a country are going to be facing this?" Provincetown board of health chair Stephen Katsurinis remembers asking other public health officials on their daily calls about the outbreak, as he pondered a future of case spike and renewed masking. "And they sort of said, 'Yeah, probably.' "

Yet leaders from Provincetown to the White House are stressing that July's events should be a cautionary tale less for the vaccinated than for the millions of Americans in parts of the country far less prepared for delta - still struggling to meet national vaccination goals, potentially more hostile to rapid containment measures for an outbreak. Only seven people with a mix of vaccination statuses were hospitalized in the Provincetown cluster, officials say, and no one has died.

"If this happened in a community that was actually under vaccinated or had a low vaccination rate," said Alex Morse, the town manager, "this would have been a very dangerous situation."

There was no "patient zero" in Provincetown, according to experts who studied the virus's spread, and no single superspreader event. Instead there were infections linked to myriad indoor spaces: Live shows, dance clubs and Airbnbs where, for instance, an entire group of seven might have contracted COVID-19, according to Katsurinis. Infections concentrated among younger men as they flocked to signature summer events like Bear Week, part of gay culture for guys on the huskier and hairier side.

Lab analysis of the first few dozen cases seemed to show that the virus spread initially among tourists, who brought the delta variant with markers suggesting it came from places including Los Angeles, Houston and Atlanta, Katsurinis said.

"Provincetown might have been the first place to really identify that delta is different," he added, "but now I think the whole country is experiencing it."

Officials argue that Provincetown was something close to a best-case scenario for living with the variant now rampant in the U.S.

While the precise vaccination rate of the thousands who crowded into Provincetown is unclear, leaders and visitors agreed that the early July crowd was unusually health-conscious. It helped that the gay community in particular, scarred by the HIV/AIDS epidemic, was hypervigilant and proactive when it came to public health measures like testing, they said.

"These weren't the people who were going out to raves to party at the height of 2020," said Brandon Echter, a 33-year-old social media strategist from Brooklyn who went to Provincetown and rated his bout of COVID-19 between a cold and flu. "These are the people that locked down, took it seriously."

As four county nurses worked to contact-trace, some attendees were already reaching out to social circles on their own. Facebook posts urged friends to get tested. In Provincetown, people lined up outside a van that was deployed in response to the outbreak and averaged several hundred free coronavirus tests each day.

Todd Buonopane, a Broadway actor and singer set to perform six dates, said he started testing himself multiple times a day in Provincetown, anxious about spreading COVID-19 at his indoor shows. On the day of his last performance, a 9 a.m. test came back negative, he said. He tested again at 5 p.m., just to be sure, even though he was fully vaccinated.

Positive.

That sent him driving six hours back to New York, where he quarantined with chills bad enough that at one point he wore a winter coat around his apartment midsummer. "The middle part of my voice is just kind of not working right now," the singer said. The whole experience left him newly cautious, even as he guesses that by now he must have "super immunity."

"I just went and got my haircut and the barber said, 'well, we can take your mask off,' " he recounted. "And I said, 'no, I'd rather leave it on.' "

Some are feeling frustration and whiplash as fears of delta fuel new guidance and mandates, but Buonopane is on board. "I'm not mad that the rules changed because, you know, the virus changed," he said.

And he is still planning to perform, with precautions: "I didn't survive Covid to not have a sold out audience," he wrote last Friday on Instagram, adding a winking emoji. Vaccines would be checked, he said, while masks were "welcome."

Provincetown held off at first on renewing pandemic restrictions. "Provincetown, like every other community in the state and in this country, around the world, are learning to live with the virus," Morse told the town Select Board on July 12, a few days before the rate of tests returning positive peaked at about 15 percent. He said he was "not recommending any change in policy at this time."

But a week later, officials turned to an indoor mask advisory. The next week it became a mandate. And the Centers for Disease Control and Prevention cited Provincetown's experience in calling for people to mask up for indoor, public settings in places with substantial spread of the coronavirus. A flood of national headlines followed.

"I think it's important to take additional precautions," Morse said this week. But he added that Provincetown still welcomes visitors and that the mandate will switch back to just guidance once the test positivity rate, now at 3.8 percent, dips below 3 percent for several days. By Thursday, the town said active cases among residents had dipped to 49.

Morse thinks people's energies are best focused on vaccination, and even highly immunized Provincetown has seen shifts since the outbreak, he said, with more businesses mandating shots for entry. Town officials worked with business groups to send out letters this week inviting venues to get certified as having immunized staff, immunized guests or both.

"Unfortunately, I think what happens in Provincetown is also dependent on what happens elsewhere, given the given the fact that thousands of people come here from all over the country," Morse said. "And the fact that we still haven't hit 50 percent of the nation being vaccinated."

That uncertainty and a heightened sense of caution hangs over people's livelihoods. Business had roared back to pre-pandemic heights this summer, with fully booked hotels and many operations struggling to fill jobs, said Radu Luca, executive director of the Provincetown Chamber of Commerce. Now, heading into a crucial month for tourism, some are struggling to keep people on payroll.

Sales last week dipped about a third from a normal year as Provincetown's outbreak really hit the national news, said Rob Anderson, chef and co-owner at a restaurant called The Canteen. Anderson worries for the town's many "call-in" seasonal workers.

"We staff up for the busiest scenario, and then if we're not going to see those numbers, then we start cutting people," said Anderson, who previously worked at newspapers including The Washington Post before pursuing a culinary career. "So I think there's only so long you can do that. At some point you'll have to let people go."

Public health experts are stressing the effectiveness of the vaccines and trying to rein in the confusion - some would say panic - over the now-subsiding case surge.

"I want to be clear: While vaccinated people can spread the virus if they get a breakthrough infection, the odds of them getting sick in the first place are far lower than those who are unvaccinated," CDC Director Rochelle Walensky said at a Monday briefing. Lucy McBride, a doctor in the District of Columbia, used her Monday newsletter to remind people that "reducing risk to zero was never on the menu" and warn that data from Provincetown had "accelerated the (inaccurate and poorly messaged) narrative that vaccinated and unvaccinated people are equally contagious.

"I think now people have to start to make their own decisions about their risk tolerance," said Katsurinis, who owns an inn where he's been fielding calls from prospective visitors wondering if they should cancel. "... I'm not comfortable saying there's a right choice or wrong choice. There's your choice."

Eckstein, the infected Provincetown visitor from Ohio, said that while the delta variant spreads, "I'm just back to the mindset that I'm not vaccinated." His friend who also traveled to the resort town, meanwhile, went on to "all the bars" in Chicago.

On the West Coast, San Diego-area psychologist Christine Baser said the Provincetown outbreak has pushed her "a few steps back into the past." She and her husband, Thomas Habib, think they caught COVID-19 during a Cape Cod trip that featured jaunts to Provincetown. Always cautious, she and her husband were both vaccinated and even wore surgical masks on their trip.

Then one morning back home about two weeks ago, Habib rubbed aftershave lotion on his hands and didn't smell a thing. He told Baser and she took a whiff of freshly ground coffee. She, too, smelled nothing.

"The hardest thing was worrying about the people we could have gotten ill," said Baser, 66. "We were waiting to see if my daughter who gave us a ride home from the airport was going to be sick, if my sister would get sick from being around my niece, if my niece's family was going to get sick. Is anybody else going to be affected by this?"

Both credit the vaccine with preventing severe sickness. Baser is recovering after cold symptoms and queasiness. Habib noticed this past weekend that he's once again detecting the scent of coffee grounds and red wine.

Hearing about Baser and Habib's experience, another couple in their 60s - who never went to Provincetown - canceled their upcoming trip to Park City, Utah.

It would have been Karen Helrich and Bertram Edelstein's first vacation since before the pandemic. Both are fully vaccinated.

"We're in that phase [of life] where we really want to go travel since we have time," Helrich said. "We want to be out and about. But we also want to live."

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The Washington Post's Carolyn Y. Johnson and Lena H. Sun contributed to this report. Dotinga reported from San Diego.