Jennifer Larson’s conversion to vaccine skeptic started after her infant son got his measles shot in October 2001. Within minutes, she said, he passed out, within hours he stopped making eye contact, within weeks he lost a sense of touch and within months he was found to have severe autism.

“Why do I connect it? Because that’s how it happened,” said the Orono mother. “Within 24 hours it was like, ‘OK, something happened to my baby!’ ”

Such vaccine horror stories slowly have been reshaping America’s public health landscape — driving down the percentage of children receiving vaccinations and allowing potentially deadly infectious diseases such as measles and whooping cough to make comebacks.

Now the skeptics are themselves facing skeptics, who blame the influence of the anti-vaccine movement for a resurgence in diseases once believed to be eradicated in the United States.

After a measles outbreak at Disneyland this winter, and then a case at the University of Minnesota, one Minnesota lawmaker said the state should make it harder for parents to skirt vaccination requirements for school admission. Doctors in some states have decided to quit treating patients who refuse vaccines.

Vaccine opponents haven’t encountered such blowback in the past, because the diseases in question have become so rare that many Americans simply didn’t worry much about them, said Kris Ehresmann, who directs immunization programs for the Minnesota Department of Health. But the national measles outbreak, even if it infects only 100 people, gave people a reason to stand up in defense of immunization, she added.

“This is the first time in about 15 years when we have been in a position, in public health, to sit back and watch the general community fight our battles for us,” she said.

Most scientists have concluded that autism isn’t caused by the MMR vaccine. Still, the impact of the anti-vaccine movement shouldn’t be underestimated, Ehresmann said. Public pressure led federal authorities to order the removal of thimerosal from vaccines other than some flu shots in 1999, despite negligible research linking the preservative to childhood disease.

And the number of parents filing conscientious objections to school-based vaccine requirements has increased steadily, even though a seminal British study claiming a link between the MMR shot and autism was debunked and then retracted in 2010.

In Minnesota, the number of parents filing such objections, while still small, increased from 607 in the 2004-2005 school year to 1,959 last year.

Unease persists, even among parents who vaccinate their kids. The Pew Research Center reported last month that just 68 percent of the general public favors mandatory vaccinations — well below the 86 percent approval rate among scientists. And a large number of parents feel vaccine safety should be at the top of the nation’s pediatric research agenda, according to 2010 survey data out of the University of Michigan.

‘They’ve heard so much’

Studies have found that vaccine skeptics are often high-achieving mothers with postgraduate degrees and careers — much like Larson, who is chief executive of an IT hardware company and a rehabilitation center for autistic children. A co-founder of the Vaccine Safety Council of Minnesota, Larson was in Washington, D.C., last week, urging Congress to schedule hearings about a federal researcher who revealed that data was removed from a key MMR vaccine safety study.

Skepticism among women might be expected, given a health care system that historically took a paternalistic attitude toward them on issues such as reproductive health, said Jigna Desai, the University of Minnesota’s chairwoman of gender, women and sexuality studies. Combine that skepticism with the instinct to protect their families, and women’s hesitance becomes clearer, even if it rests on pseudoscience, she added.

“A lot of these women who are vaccine-hesitant hear there is a risk, and they think, ‘Why should I take a risk? My job is to protect my family,’ ” said Desai, who has studied the anti-vaccine movement. “Measles was eliminated as a disease in the United States around 2000, so they feel like it’s not something they have to worry about. But things like autism feel very real.”

The anti-vaccine movement also draws government skeptics, who suspect ulterior motives behind vaccine rules, and naturalists who worry about vaccines just as they worry about food preservatives.

“They’re afraid. They’ve read so much. They’ve heard so much. They’re very confused,” said Patsy Stinchfield, an infectious disease expert at Children’s Hospitals and Clinics of Minnesota. “They might be risk-averse, and this whole notion of doing something — of subjecting my child to something like this vaccine — seems like an error of commission rather than omission.”

Tales such as Larson’s are central to skeptics. The immediacy with which her son changed after the MMR shot has Larson convinced it caused his autism. Similarly, Abdirizak Jama of Minneapolis said his son started having seizures on the 15-minute drive home from the clinic where he received an MMR vaccine in 2005. The boy who was the smartest of his sons suddenly stopped talking and later received an autism diagnosis.

Vaccine suspicions have been strong in the Somali community, which has suffered an unusually high and, so far, unexplained rate of autism in its American-born children. Jama couldn’t bear to vaccinate his next two children. He had lived through measles as a 6-year-old in Somalia, and it was nothing compared to autism.

“I witnessed this experience, with my eyes, the change in him,” he said.

Ehresmann said such stories only reveal coincidences, not causes. She pointed out that children normally receive MMR shots at a key stage in their development when deficits in speech and motor skills can reveal the first signs of autism.

Still it’s a mistake for public health officials to rely on statistics in the face of such stories, she said. “If you hear a story that this happened to somebody — man, that can really impact your thinking.”

But wrenching personal tales from the other side of the vaccine debate are now emerging — from parents of children too fragile to be vaccinated. They need others to be vaccinated to stop the spread of disease for which their kids lack a defense.

The parents of Ben Bredesen had to delay his second dose of MMR vaccine when he was 2 — he had leukemia, and chemotherapy had eroded his immune system.

When Ben was 3, his family lived a nightmare for 21 days when he was potentially exposed during a hospital visit to an unvaccinated child who had measles.

The episode was in some ways more intense than Ben’s cancer therapy, said his mother, Laura Bredesen, of Independence. “It was a sense of urgency, a fear that this will be a life-or-death situation if he comes out with measles.”

Bredesen has since become a public advocate for vaccination. Her son, now 7, is cancer-free and was finally able to get revaccinated.

Study retracted

The great bulk of medical studies find no link between vaccines and autism.

Vaccine critics point to a 2014 disclosure by a scientist with the U.S. Centers for Disease Control and Prevention that a group of black children was removed from a key 2004 study dispelling a link between MMR vaccine and autism. Federal officials responded that the children were removed due to incomplete birth records. Another researcher added them back into a reanalysis of the data last fall, which showed a more than twofold increase in autism among vaccinated black children by age 3.

However, the small medical journal that published the study since has retracted it, in part because the author is the parent of an autistic child who believes in the vaccine-autism link. Problems with the statistical analysis also undermined his findings.

Larson still wants congressional hearings to learn why potentially important data was held out of the original study in the first place.

“I’m just saying parents need to know the risks,” she said. “There are risks, there are benefits, but the government needs to be honest about them.”

MMR vaccine packaging already lists a variety of rare complications, including seizures and a swelling of the brain known as encephalitis. The federal government acknowledges complications, both through a vaccine-adverse event reporting system and a compensation fund it created to shield manufacturers from liability but financially support people injured by vaccines.

To Stinchfield, the persistence of vaccine conspiracies suggests that doctors should try harder to listen to parents, and then put the rare but known risks in proper context — which often is lacking on the Internet.

“For whatever reason, people are more comfortable following the recommendations of some unknown person on an Internet blog than they are of their own health care provider,” she said. “What we as clinicians need to do is continue to build that relationship and build that trust back with our patients.”