Stephanie Nana, an evangelical Christian in Edmond, Okla., refused to get a Covid-19 vaccine because she believed it contained “aborted cell tissue.”

Nathan French, who leads a nondenominational ministry in Tacoma, Wash., said he received a divine message that God was the ultimate healer and deliverer: “The vaccine is not the savior.”

Lauri Armstrong, a Bible-believing nutritionist outside of Dallas, said she did not need the vaccine because God designed the body to heal itself, if given the right nutrients. More than that, she said, “It would be God’s will if I am here or if I am not here.”

The deeply held spiritual convictions or counterfactual arguments may vary. But across white evangelical America, reasons not to get vaccinated have spread as quickly as the virus that public health officials are hoping to overcome through herd immunity.

The opposition is rooted in a mix of religious faith and a longstanding wariness of mainstream science, and it is fueled by broader cultural distrust of institutions and gravitation to online conspiracy theories. The sheer size of the community poses a major problem for the country’s ability to recover from a pandemic that has resulted in the deaths of half a million Americans. And evangelical ideas and instincts have a way of spreading, even internationally.

There are about 41 million white evangelical adults in the U.S. About 45 percent said in late February that they would not get vaccinated against Covid-19, making them among the least likely demographic groups to do so, according to the Pew Research Center.

“If we can’t get a significant number of white evangelicals to come around on this, the pandemic is going to last much longer than it needs to,” said Jamie Aten, founder and executive director of the Humanitarian Disaster Institute at Wheaton College, an evangelical institution in Illinois.

As vaccines become more widely available, and as worrisome virus variants develop, the problem takes on new urgency. Significant numbers of Americans generally are resistant to getting vaccinated, but white evangelicals present unique challenges because of their complex web of moral, medical, and political objections. The challenge is further complicated by longstanding distrust between evangelicals and the scientific community.

“Would I say that all public health agencies have the information that they need to address their questions and concerns? Probably not,” said Dr. Julie Morita, the executive vice president of the Robert Wood Johnson Foundation and a former Chicago public health commissioner.

No clear data is available about vaccine hesitancy among evangelicals of other racial groups. But religious reasoning often spreads beyond white churches.

Many high-profile conservative pastors and institutional leaders have endorsed the vaccines. Franklin Graham told his 9.6 million Facebook followers that Jesus would advocate for vaccination. Pastor Robert Jeffress commended it from an anti-abortion perspective on Fox News. (“We talk about life inside the womb being a gift from God. Well, life outside the womb is a gift from God, too.”) The president of the Southern Baptist Convention, J.D. Greear, tweeted a photo of himself receiving a shot.

But other influential voices in the sprawling, trans-denominational movement, especially those who have gained their stature through media fame, have sown fears. Gene Bailey, the host of a prophecy-focused talk show on the Victory Channel, warned his audience in March that the government and “globalist entities” will “use bayonets and prisons to force a needle into your arm.” In a now-deleted TikTok post from an evangelical influencer’s account that has more than 900,000 followers, she dramatized being killed by authorities for refusing the vaccine.

Dr. Simone Gold, a prominent Covid-19 skeptic who was charged with violent entry and disorderly conduct in the Jan. 6 Capitol siege, told an evangelical congregation in Florida that they were in danger of being “coerced into taking an experimental biological agent.”

The evangelical radio host Eric Metaxas wrote “Don’t get the vaccine” in a tweet on March 28 that has since been deleted. “Pass it on,” he wrote.

Some evangelicals believe that any Covid restrictions — including mask mandates and restrictions on in-person church worship — constitute oppression.

And some have been energized by what they see as a battle between faith and fear, and freedom and persecution.

“Fear is the motivating power behind all of this, and fear is the opposite of who God is,” said Teresa Beukers, who travels throughout California in a motor home. “I violently oppose fear.”

Ms. Beukers foresees severe political and social consequences for resisting the vaccine, but she is determined to do so. She quit a job at Trader Joe’s when the company insisted that she wear a mask at work. Her son, she said, was kicked off his community college football team for refusing Covid testing protocols.

“Go ahead and throw us in the lions’ den, go ahead and throw us in the furnace,” she said, referring to two biblical stories in which God’s people miraculously survive persecution after refusing to submit to temporal powers.

Jesus, she added, broke ritual purity laws by interacting with lepers. “We can compare that to people who are unvaccinated,” she said. “If they get pushed out, they’ll need to live in their own colonies.”

One widespread concern among evangelicals is the vaccines’ ties to abortion. In reality, the connection is remote: Some of the vaccines were developed and tested using cells derived from the fetal tissue of elective abortions that took place decades ago.

The vaccines do not include fetal tissue, and no additional abortions are required to manufacture them. Still, the kernel of a connection has metastasized online into false rumors about human remains or fetal DNA being an ingredient in the vaccines.

Some evangelicals see the vaccine as a redemptive outcome for the original aborted fetus.

Some Catholic bishops have expressed concerns about the abortion link, too. But the Vatican has concluded the vaccines are “morally acceptable,” and has emphasized the immediate danger posed by the virus. Just 22 percent of Catholics in America say they will not get the vaccine, less than half the share of white evangelicals who say that.

White evangelicals who do not plan to get vaccinated sometimes say they see no need, because they do not feel at risk. Rates of Covid-19 death have been about twice as high for Black, Hispanic, and Native Americans as for white Americans.

White pastors have largely remained quiet. That’s in part because the wariness among white conservative Christians is not just medical, but also political. If white pastors encourage vaccination directly, said Dr. Aten, “there are people in the pews where you’ve just attacked their political party, and maybe their whole worldview.”

Dr. Morita, of the Robert Wood Johnson Foundation, said the method to reach white evangelicals is similar to building vaccine confidence in other groups: Listen to their concerns and questions, and then provide information that they can understand from people they trust.

But a public education campaign alone may not be enough.

There has been a “sea change” over the past century in how evangelical Christians see science, a change rooted largely in the debates over evolution and the secularization of the academy, said Elaine Ecklund, professor of sociology and director of the Religion and Public Life Program at Rice University.

There are two parts to the problem, she said: The scientific community has not been as friendly toward evangelicals, and the religious community has not encouraged followers to pursue careers in science.

Distrust of scientists has become part of cultural identity, of what it means to be white and evangelical in America, she said.

For slightly different reasons, the distrust is sometimes shared by Asian, Hispanic and Black Christians, who are skeptical that hospitals and medical professionals will be sensitive to their concerns, Dr. Ecklund said.

“We are seeing some of the implications of the inequalities in science,” she said. “This is an enormous warning of the fact that we do not have a more diverse scientific work force, religiously and racially.”

Among evangelicals, Pentecostal and charismatic Christians may be particularly wary of the vaccine, in part because their tradition historically emphasizes divine health and miraculous healing in ways that can rival traditional medicine, said Erica Ramirez, a scholar of Pentecostalism and director of applied research at Auburn Seminary. Charismatic churches also attract significant shares of Black and Hispanic Christians.

Dr. Ramirez compares modern Pentecostalism to Gwyneth Paltrow’s Goop, with the brand’s emphasis on “wellness” and “energy” that infuriates some scientists: “It’s extra-medical,” she said. “It’s not anti-medical, but it decenters medicine.”

The Centers for Disease Control and Prevention and Dr. Anthony Fauci are not going to be able to persuade evangelicals, according to Curtis Chang, a consulting professor at Duke Divinity School who is leading an outreach project to educate evangelicals about the vaccine.

The project includes a series of short, shareable videos for pastors, answering questions like “How can Christians spot fake news on the vaccine?” and “Is the vaccine the Mark of the Beast?” The latter refers to an apocalyptic theory that the AntiChrist will force his sign onto everyone at the end of the world.

These are questions that secular public health entities are not equipped to answer, he said. “The even deeper problem is, the white evangelicals aren’t even on their screen.”

Mr. Chang said he recently spoke with a colleague in Uganda whose hospital had received 5,000 vaccine doses, but had only been able to administer about 400, because of the hesitancy of the heavily evangelical population.

“How American evangelicals think, write, feel about issues quickly replicates throughout the entire world,” he said.

At this critical moment, even pastors struggle to know how to reach their flocks. Joel Rainey, who leads Covenant Church in Shepherdstown, W.Va., said several colleagues were forced out of their churches after promoting health and vaccination guidelines.

Politics has increasingly been shaping faith among white evangelicals, rather than the other way around, he said. Pastors’ influence on their churches is decreasing. “They get their people for one hour, and Sean Hannity gets them for the next 20,” he said.

Mr. Rainey helped his own Southern Baptist congregation get ahead of false information by publicly interviewing medical experts — a retired colonel specializing in infectious disease, a church member who is a Walter Reed logistics management analyst, and a church elder who is a nurse for the Department of Veterans Affairs.

On the worship stage, in front of the praise band’s drum set, he asked them “all of the questions that a follower of Jesus might have,” he said later.

“It is necessary for pastors to instruct their people that we don’t always have to be adversaries with the culture around us,” he said. “We believe Jesus died for those people, so why in the world would we see them as adversaries?”