Circus performer Kristen Teffeteller had finally gotten back onstage when the pandemic made her jump through yet another hoop. Her show at Skull’s Rainbow Room in Nashville, which had been shut down for more than a year, returned in early June to packed crowds of tourists. It felt great to be onstage. It felt great to be on a payroll.

Well, for now.

When Teffeteller saw that the Centers for Disease Control and Prevention was reissuing mask recommendations for vaccinated people in certain circumstances — including being in a room with unvaccinated people, like her intimate performance venue — she began to wonder if her hoop act would go back into hibernation.

“The show hasn’t even been back two months,” says Teffeteller, 37.

This particular brand of disappointment felt both familiar and novel. Maybe because she had finally allowed herself to hope that things had actually gotten back on track.

“It kind of feels like we’re sliding a few steps backwards,” she says. “That light that we thought we were seeing at the end of the tunnel is now not so much light anymore.”

Here we go again. Instead of flattening the curve, we’ve hit the delta swerve: Cases, mostly among the unvaccinated, are climbing once more. Masks are back. Fights about masks are back. People who thought they were finally catching a break are catching breakthrough infections. So much for returning to the office. So much for Shot Girl Summer. Vaxxed, waxed, but definitely not relaxed.

“We just have to get ourselves mentally prepared,” says Kimberly Justice, 47, a project coordinator in Chicago. After two months of not wearing a mask — weird at first, but then freeing, she says — she’s gearing back up again for whatever comes next. She has asthma.

“I just stocked up on some new masks, disposable ones,” she says. “Just in case.”

She can’t believe we’re doing this again.

“You follow the guidelines by the CDC and your local government only to be back where we started,” says Justice. “So it’s a little bit frustrating.”

After a few carefree weeks of letting our collective guard down, the sudden plunge back into the pandemic lifestyle is giving people whiplash. Google and Apple employees who were preparing to return to the office have been told to wait another month. Disney World went back to requiring masks for all guests indoors, regardless of vaccination status.

Joanna Kempner, a sociology professor at Rutgers University, was cautious all year long, and postponed a trip to see family and friends on the West Coast. After she and her adult family members were vaccinated and caseloads had plummeted, the time finally seemed right. So she and her husband and their two kids — too young to be vaccinated, at 7 and 11 — got on a plane to San Francisco. They went on a hike with friends who were being just as cautious as they were. Less than a day later, her friend’s kid had tested positive for the coronavirus, and her daughter started feeling ill the day after. Then, the whole family started quarantining in a Lake Tahoe vacation home, awaiting their test results, wearing masks and staying away from Kempner’s parents, who are in the house with them. So much for that. (The family later tested negative.)

There are bigger tragedies, Kempner knows. But “what makes me angry is that part of the calculation was that vaccines were available to everyone, and the grown-ups haven’t done what they were supposed to do,” she says. “My kids did what they were supposed to do.” She can’t stand to think of them potentially having to do more virtual school in the fall.

And the brides. Oh, the brides. Tiffany Renee Balmer is the CEO of a D.C. wedding planning company. She’s worried about her couples “who have rescheduled their wedding for the third and fourth time, and what that will look like if they have to reschedule it again,” she says. “And just all the emotions.”

Invitations for fall weddings are going out in the mail imminently, and planners are hopeful that things will be okay. If event sizes become restricted once again, Stephanie Sadowski, another D.C.-area wedding planner, doesn’t think couples have it in them to send out yet another “Change the Date.”

“I think they will cancel,” she says.

Balmer is staying on the balls of her feet, ready for anything. “If we have to change things up, if we have to find an outdoor venue, if we have to plan this wedding for the fifth time — whatever has to be done will just be done,” she says. It’s exhausting.

The best way to describe what we’re going through right now is the prisoner’s dilemma, says Gretchen Chapman, a professor of psychology who studies vaccination decision-making at Carnegie Mellon University. Vaccines, as with the classic game theory model, provide a collective reward when everyone cooperates, though individuals may have personal incentives not to cooperate. If not enough individuals cooperate, then the people who did the right thing suffer the consequences.

“In social dilemmas, people really do not like being the sucker,” says Chapman. “They do not like to cooperate when the other person has defected.”

In fact, Chapman says that in prisoner’s dilemma experiments, people who are given opportunities to punish the defectors — usually financially — often do so, even if it means they lose some of their winnings in the process.

“There’s also some interesting experiments showing that sending an angry note to the other person is almost as good, or sometimes even preferable, to actually taking money away from them,” says Chapman. “What you really want to do is send them the message that you screwed up.” Which explains Twitter right now.

Chapman is personally frustrated, too.

“It’s sort of like watching a car crash in slow motion,” she says. “You know what’s going to happen and you’re powerless to stop it.”

Here’s another metaphor, from an E.R. nurse in central Virginia who spoke on the condition of anonymity because he is not authorized to speak to reporters: “A floor can look solid, and then you put your foot on it and you find out that termites have been at the foundation, so you go straight through the floorboards,” he says. “That’s the way that I feel about it right now.”

His delta swerve feels worse than the pandemic wall of last January. The hospital is understaffed because many nurses, burned out from the last year and a half, have left to find less stressful jobs, so a smaller staff is treating a huge wave of patients. And the covid patients he gets — typically unvaccinated — are often in denial.

“I’ve had people say, ‘Well, that can’t be right,’ ” when he delivers their positive test results, he says. Sometimes, they yell at him. “We’re easy targets because we’re right there.”

Chapman is not optimistic that the more than 40 percent of eligible Americans who have not yet received any dose of vaccine will all be swayed.

“Trying to change people’s beliefs and feelings is, on average, not very effective at getting people to change their vaccination behavior,” she says. What does work are requirements: when France approved a law that only vaccinated people could enter certain restaurants, entertainment venues and intercity transportation, vaccine-booking platforms recorded a surge in appointments. Some U.S. employers, including health care systems, schools, and tech companies, have made vaccination a requirement of employment. According to CNN, this week’s first shot vaccination rate is 35 percent higher than the week before.

But the swerve is already here. We were all too busy dining indoors and going on vacation to notice. Not the E.R. nurse: He saw it coming.

“I would have loved to have been wrong,” he says. “I would have relished that.”

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