They Waited, They Worried, They Stalled. This Week, They Got the Shot.

CHICAGO — They acknowledged that they could have showed up months ago. Many were satisfied that they were finally doing the right thing. A few grumbled that they had little choice.

On a single day this past week, more than half a million people across the United States trickled into high school gymnasiums, pharmacies and buses converted into mobile clinics. Then they pushed up their sleeves and got their coronavirus vaccines.

These are the Americans who are being vaccinated at this moment in the pandemic: the reluctant, the anxious, the procrastinating.

The people being vaccinated now are not members of the eager crowds who rushed to early appointments. But they are not in the group firmly opposed to vaccinations, either.

Instead, they occupy a middle ground: For months, they have been unwilling to receive a coronavirus vaccine, until something or someone — a persistent family member, a work requirement, a growing sense that the shot was safe — convinced them otherwise.

How many people ultimately join this group, and how quickly, could determine the course of the coronavirus in the United States.

Some of the newly vaccinated said they made the decision abruptly, even casually, after months of inaction. One woman in Portland, Ore., was waiting for an incentive before she got her shot, and when she heard that a pop-up clinic at a farmers’ market was distributing $150 gift cards, she decided it was time. A 60-year-old man in Los Angeles spontaneously stopped in for a vaccine because he noticed that for once, there was no line at a clinic. A construction worker said his job schedule had made it difficult to get the shot.

Many people said they had arrived for a vaccine after intense pressure from family or friends.

“‘You’re going to die. Get the Covid vaccine,’” Grace Carper, 15, recently told her mother, Nikki White, of Urbandale, Iowa, as they debated when they would get their shots. Ms. White, 38, woke up on Thursday and said she would do it. “If you want to go get your vaccine, get up,” Ms. White told her daughter, who was eager for the shot, and the pair went together to a Hy-Vee supermarket.

Others were moved by practical considerations: plans to attend a college that is requiring students to be vaccinated, a desire to spend time socializing with high school classmates, or a job where unvaccinated employees were told to wear masks. Their answers suggest that the mandates or greater restrictions on the unvaccinated that are increasingly a matter of debate by employers and government officials could make a significant difference.

Audrey Sliker, 18, of Southington, Conn., said she got a shot because New York’s governor announced that it was required of all students attending State University of New York schools. She plans to be a freshman at SUNY Cobleskill this fall.

“I just don’t like needles, in general,” she said, leaving a white tent that housed a mobile vaccination site in Middlefield, Conn. “So it’s more like, ‘Do I need to get it?’”

Many people interviewed described their choices in personal, somewhat complicated terms.

Willie Pullen, 71, snacked on a bag of popcorn as he left a vaccination site in Chicago, one of the few people who showed up there that day. He was not opposed to the vaccines, exactly. Nearly everyone in his life was already vaccinated, he said, and though he is at greater risk because of his age, he said he believed he was healthy and strong enough to be able to think on it for a while.

What pushed him toward a high school on the West Side of Chicago, where free vaccines were being administered, was the illness of the aging mother of a friend. Mr. Pullen wanted to visit her. He felt it would be irresponsible to do so unvaccinated.

“I was holding out,” Mr. Pullen said. “I had reservations about the safety of the vaccine and the government doing it. I just wanted to wait and see.”

‘I’m still not sure if it’s safe’

The campaign to broadly vaccinate Americans against the coronavirus began in a roaring, highly energetic push early this year, when millions were inoculated each day and coveted vaccine appointments were celebrated with joyful selfies on social media. The effort peaked on April 13, when an average of 3.38 million doses were being administered in the United States. The Biden administration set a goal to have 70 percent of American adults at least partly vaccinated by July 4.

But since mid-April, vaccinations have steadily decreased, and in recent weeks, plateaued. Weeks after the July 4 benchmark has passed, the effort has now dwindled, distributing about 537,000 doses each day on average — about an 84 percent decrease from the peak.

About 68.7 percent of American adults have received at least one shot. Conservative commentators and politicians have questioned the safety of the three vaccines that the Food and Drug Administration has approved for emergency use, and in some parts of the country, opposition to inoculation is tied to politics. An analysis by The New York Times of vaccine records and voter records in every county in the United States found that both willingness to receive a coronavirus vaccine and actual vaccination rates were lower, on average, in counties where a majority of residents voted to re-elect Donald J. Trump.

In Florida, a clinic in Sarasota County was quiet, a brightly lit waiting area full of mostly empty chairs. Several people wandered in, often no more than one or two in an hour. Lately, they are vaccinating fewer than 30 people there a day.

Elysia Emanuele, 42, a paralegal, came for a shot. One factor in her decision had been the rising case numbers in the state, which she had been watching with worry.

“If everything had gone smoothly, if we had shut down immediately and did what we needed to do and it was seemingly wiped out,” she said, “I think I would have been less likely to get the vaccine.”

In the shade of a freeway underpass in South Los Angeles, volunteers and would-be vaccine patients tried to talk over the roar of passing cars.

Ronald Gilbert, 60, said he did not really believe in the vaccines and has never been a fan of needles, but with an uptick in cases he reasoned that it was “better to be safe than sorry.”

“I feel better having this now, seriously I do,” he said. “I’m going to be walking like a rooster, chest up, like ‘You got the vaccine? I got the vaccine.’”

News of the Delta variant also changed the mind of Josue Lopez, 33, who had not planned on getting a vaccine after his whole family tested positive for the coronavirus in December.

“I thought I was immune, but with this variant, if it’s more dangerous, maybe it’s not enough,” he said. “Even now, I’m still not sure if it’s safe.”

‘We have to fight for every one of them’

At a vaccination site at Malcolm X College in Chicago, Sabina Richter, one of the workers there, said it used to be easy to find people to get shots. More recently, they had to offer incentives: passes to an amusement park in the north suburbs and Lollapalooza.

“Some people come in and they’re still hesitant,” she said. “We have to fight for every one of them.”

Cherie Lockhart, an employee at a care facility in Milwaukee for older and disabled people, said she was worried about the vaccines because she did not trust a medical system that she felt had always treated Black people differently.

She was not anti-vaccine, she said, just stalling until something could help her be sure. Her mother ultimately convinced her.

“My mom has never steered me wrong,” Ms. Lockhart, 35, said. “She said, ‘I feel this is right in my heart of hearts.’ So I prayed about it. And, ultimately, I went with my guiding light.”

Many of the people who newly sought shots said they had wanted to see how the vaccines affected Americans who rushed to get them early.

“I do know people who have gotten it and they haven’t gotten sick, so that’s why,” said Lisa Thomas, 45, a home health care worker from Portland, Ore. “I haven’t heard of any cases of anyone hurting from it, and there’s a lot to benefit from it.”

For Cindy Adams, who works for a Des Moines insurance company, it was her job’s requirement to wear a mask as an unvaccinated person that pushed her into the Polk County Health Department drive-up clinic for her first dose of the Pfizer-BioNTech vaccine.

Ms. Adams, 52, said she had been concerned about possible long-term effects of the vaccines. But now her husband, children and most of her extended family have been vaccinated, as have most of her co-workers.

“I just honestly got sick of wearing the mask,” Ms. Adams said. “We had an event yesterday, and I had to wear it for five hours because I was around a lot of people. And I was sick of it.

“Everyone else is healthy and hasn’t had any side effects, gravely, yet, so I decided I might as well join the crowd.”

Julie Bosman reported from Chicago. Contributing reporting were Matt Craig from Los Angeles, Elizabeth Djinis from Sarasota, Fla., Timmy Facciola from Middlefield, Conn., Ann Hinga Klein from Des Moines, Emily Shetler from Portland, Ore., and Dan Simmons from Milwaukee.