They were required to get vaccinated because of their jobs. They refused.

Under the threat of losing their jobs, hundreds of thousands of New Yorkers finally got a Covid-19 vaccine. Teachers, nurses and home health aides accepted their occupations’ mandates. The mass resignations some experts had predicted did not occur, as most workers hurriedly got inoculated.

Josephine Valdez, 30, a public school paraprofessional from the Bronx, did not.

Failing to meet the New York City Education Department’s vaccination deadline, Ms. Valdez lost her job this month. She is among the 4 percent of the city’s roughly 150,000 public school employees who did not comply with the order.

She is also part of a sizable, unwavering contingent across the United States whose resistance to the vaccines have won out over paychecks, or who have given up careers entirely.

This month, Washington State University fired its top football coach and several other members of the team’s staff after they refused to get vaccinated. In Massachusetts, where a state mandate took effect this past week, at least 150 state police officers resigned or filed paperwork signaling plans to do so.

Their resistance goes against reams of scientific data showing that the Covid-19 vaccines are overwhelmingly safe and effective and have reduced hospitalizations and deaths.

To public health officials, and the majority of Americans, the defiance is unreasonable and incomprehensible. Who would jeopardize their families’ financial security over a shot that has been proven safe and effective at preventing death?

That is not the way the holdouts see it. In interviews, New Yorkers who have given up their livelihoods spoke of their opposition to the vaccines as rooted in fear or, more commonly, in a deeply held conviction — resistance to vaccination as a principle to live by, one they put above any health, job or financial consideration.

It is this alternative worldview, resistant to carrot or stick, that helps explain why 21 percent of eligible adults in the country, have not gotten a single vaccine dose, threatening a nationwide goal of achieving herd immunity.

The mandates, which many resisters balk at as unheard-of government overreach, are similar to those that have been instituted in the past for schoolchildren for diseases like polio, mumps and measles.

And the mandates appear to be working. About 84 percent of adult New Yorkers have now received at least one vaccine dose in the face of state and city mandates, as well as requirements imposed by some private companies.

Last week, Mayor Bill de Blasio announced that nearly all 300,000 of the city’s employees would have to a first shot by Nov. 1. The order puts pressure on New York City’s approximately 46,000 municipal employees who have not yet done so.

Those who are holding out cite different reasons for their choice: The vaccines are too new, too risky, pumped out too quickly, some said. Others cited their religious faith. More, citing what they say are American values of independence, refused in part because they objected to being forced.

Still, misinformation has been powerful, and fear and doubt have hardened into obstinacy for many of the vaccine refusers.

As Ms. Valdez packed up her classroom on her final day, Oct. 1, her students became distressed, she recalled.

“The kids, they were telling me not to leave, to just go get the vaccine,” said Ms. Valdez, who has moved back in with her parents. “I had to explain to them, the government doesn’t own my body.”

She is now tutoring an elementary school student whose parents chose to remove their daughter from public school because they oppose the mask requirement for children.

Theresa Malek, 38, nurse

This month, Theresa Malek packed up her car, said goodbye to her husband and three children and drove from Sloan, N.Y., in the western part of the state, to Atlanta for her new job as a travel nurse.

Ms. Malek, who was previously a nurse at Erie County Medical Center in Buffalo, refused vaccination and resigned last month. She is her family’s sole breadwinner, she said, and will be working at an Atlanta hospital on shifts that can last two months at a time.

“I’ve had anxiety attacks, crying, I’m a hot mess,” said Ms. Malek, who chose not to get vaccinated because she fears possible side effects. “I don’t want to walk away from this career. I don’t want to walk away from these people who need us. But I also need to know that I am going to be healthy.”

According to the Centers for Disease Control and Prevention, the most common effects of Covid-19 vaccines can include headaches, nausea and fatigue. More severe side effects have been reported in rare cases.

For four months at the start of the pandemic, Ms. Malek lived alone at her home in Sloan while her husband and children lived with her in-laws so she could avoid the possibility of exposing them to the virus because of her work. Some of her extended family has pushed her to get vaccinated.

Ayse Ustares, 47, school social worker

“I’ve dedicated my whole life to helping kids,” said Ayse Ustares, a school social worker who is a 20-year veteran of New York City’s schools. She said she had refused to get vaccinated because she had been sick with Covid-19 and believes she now has natural immunity.

Dr. Dave A. Chokshi, New York City’s health commissioner, said that studies showed that vaccination strengthens immunity for those who had a prior infection.

“Using the evidence we have right now about benefits and risks of vaccination, regardless of prior Covid-19, the choice is clear,” he said in a statement. “Get the shot!”

Ms. Ustares, who lives in Dobbs Ferry, N.Y., in Westchester County, is on unpaid leave from the Education Department because she has not complied with the order.

“What’s the biggest fear in America?” she said. “Money. They think: ‘Hit people in the wallet.’ So many of my friends caved, they were just like me, but now they are coerced into taking the shot, just so they can make their mortgage payment. I have already let go of the fear.”

Ms. Ustares is exploring new avenues, including opening a gymnasium that would help children develop motor skills, she said.In her view, mandatory vaccination is a step toward other choices being taken away.

“It is not going to stop here,” she said. “The more we comply, the more they are going to take. First it’s the masks, then it’s the weekly testing, then it’s the vaccine,” then booster shots.

Itzia Jimenez, 33, gym cleaner

This summer, Mr. de Blasio introduced vaccine mandates for certain activities, including indoor dining and gyms. Itzia Jimenez, who refused to get vaccinated because she fears the vaccines are not safe, lost her job cleaning gyms.

Ms. Jimenez said she has struggled to find cleaning jobs because she is unvaccinated. Her family now relies financially on her daughter’s father, whose workplace required him to be vaccinated.

She is making plans to home-school her preteen daughter, she said, anticipating a possible future mandate for public school children. All 50 states already require certain vaccinations, such as for measles, mumps and rubella. This month, California announced plans to require Covid-19 vaccines for students. Eric Adams, New York City’s likely next mayor, has indicated he plans to do the same.

“But she likes to be around her friends, it is so hard for her,” Ms. Jimenez said of her daughter. “Am I doing the right thing, am I doing the correct thing?”

Douglas Kariman, 48, nurse

A nurse in a medical intensive care unit at Erie County Medical Center, Douglas Kariman applied for a religious exemption from mandatory vaccination. A Baptist Christian, he said his opposition to abortion was one factor in his refusing the vaccines, which, like aspirin, ibuprofen and many other medicines, were developed using research from fetal cells collected decades ago.

At one health care network in Arkansas, the Conway Regional Health System, so many employees requested religious exemptions that the system began requiring them to sign a form stating that their faith also prevented them from using 30 common medicines, including Benadryl and Tums, that were developed using research from fetal cells, according to reports.

New York State’s mandate for health workers did not permit religious exemptions, but this month, a federal judge in Utica issued a temporary stay after a group of medical workers seeking such exemptions filed suit; Mr. Kariman remains employed pending the resolution of the case.

He said he knows how dangerous the coronavirus is.

“I’m not one of these anti-vaxxers as a whole saying, ‘It’s fake.’ It’s not fake,” he said. “I feel very strongly you can get sick and you can die from this. I took care of people who died from this.”

According to C.D.C. data, unvaccinated people are 4.5 times more likely to contract the coronavirus, and 11 times more likely to die from their infection than those who are vaccinated.

Crisleidy Castillo, 27, elementary schoolteacher

Crisleidy Castillo, who was a special-education teacher in the Bronx, said she refused to get vaccinated because she was still breastfeeding her daughter and had concerns because the vaccine had not been tested on women who were breastfeeding.

The C.D.C., saying that antibodies passed through breast milk can help protect babies, recommends vaccination for those who are breastfeeding, although study data is limited.

“When you’re breastfeeding, they say, ‘Oh, you cannot drink coffee, you cannot drink alcohol,’” Ms. Castillo said. “I’m not going to feel pressure to do something that I don’t want to do.”

Four days after she lost her public school job, she was hired to teach first grade at a private school in Westchester County where vaccination is recommended but not required. But the pay is about 60 percent less than her previous salary, she said, forcing her to take her son out of day care because she can no longer afford it. Her family is also no longer covered by her health insurance.

Sharon Otterman contributed reporting.