Nurse Lydia Fulton prepares to administer the measles, mumps and rubella vaccine and a vaccine used to help prevent diphtheria, pertussis, tetanus and polio at Children's Primary Care Clinic in Minneapolis in April. (Courtney Perry for The Washington Post)

Minnesota’s worst measles outbreak in decades has un­expectedly energized anti-vaccine forces, who have stepped up their work in recent months to challenge efforts by public health officials and clinicians to prevent the spread of the highly infectious disease.

In Facebook group discussions, local activists have asked about holding “measles parties” to expose unvaccinated children to others infected with the virus so they can contract the disease and acquire immunity. Health officials say they are aware of the message posts but haven’t seen evidence that such parties are taking place.

The activists also are using social media to urge families who do not want to immunize their children or who believe their children have been harmed by vaccines to meet in Minneapolis this week with associates of Andrew Wakefield, the founder of the modern anti-vaccine movement. The associates have been touring the United States and abroad with the former doctor’s movie, “Vaxxed: From Cover-up to Catastrophe,” which repeats the debunked theory that vaccines cause autism and that scientists, pediatricians and the public health system are part of an elaborate conspiracy. A recent fundraiser at the clinic of a suburban Minneapolis pediatrician who supports “alternative vaccine schedules” benefited a second film that also will feature Wakefield, whose research has been retracted for falsehoods.

Here are some of the most common arguments for and against vaccination. (The Washington Post)

The activity in Minnesota has taken some immunization supporters and clinicians by surprise.

“I’m shocked by how emboldened they’ve gotten,” said Karen Ernst, executive director of Voices for Vaccines, a national parent-led group that advocates for vaccination. “I think most people thought the anti-vaccine voices would sit home and lay low. . . . Instead, they became more public, they did more outreach.”

She and others are worried about the potential impact elsewhere.

Other states should be on alert, as these Minnesota anti-vaxxers have reach across the country” through families, schools and lawmakers, Ernst said. “And they have the money to help mobilize and finance their agenda in any other state.”

Patti Carroll, director of outreach for the Vaccine Safety Council of Minnesota, has said a goal is to give parents more information, including about their right to refuse to vaccinate. She did not respond to The Washington Post’s emailed questions about the council’s current efforts. But an affiliated group, the Minnesota Vaccine Freedom Coalition, posted the questions on its Facebook page on Wednesday and added responses.

“We are a community and advocacy group,” the post said. “We socialize, we support each other, we learn together and we lobby to protect health choice rights.”

Craig Egan of Tacoma, Wash., debates the need for childhood vaccinations with a representative of Montana for Vaccine Choice during a July stop of a nationwide bus tour connected to the anti-vaccine movie “Vaxxed.” Egan said he was following the tour to protest at each of its stops. (Al Knauber/Helena (Mont.) Independent Record)

Since the outbreak began in late March, Minnesota public health officials have confirmed 79 local measles cases. Most involved unvaccinated preschool children in the Somali American community. More than 8,200 people were exposed in day-care ­clinics, schools, and hospitals. Twenty-two people were hospitalized, many with high fever, breathing difficulties and dehydration. There have been no deaths, although the disease can be fatal.

The most recent case was reported July 13 and involved a white young adult who was never vaccinated because of parental objections. Health authorities need to wait two incubation periods — 42 days — before declaring the outbreak over. That could happen Aug. 25 if no one else gets sick.

Despite the anti-vaccine drumbeat, Minnesota’s Somali American community has begun to push back, according to some health-care providers. As part of an unprecedented collaboration clinicians and public health officials launched this summer, ­Somali American imams are urging families to protect their children by getting the measles-mumps-rubella (MMR) vaccine.

Engaging the imams and trusted providers has made an enormous difference, said Patsy Stinchfield, a pediatric nurse practitioner and infection-control expert who has led the outbreak response at the Children’s Minnesota hospital. “We have seen a major shift in the uptake of Somali families coming in for MMR.”

Doctors now are seeing parents who had previously refused — sometimes repeatedly — to have their children inoculated. They “are still somewhat cautious or hesitant,” said Paula Mackey, a pediatrician at a Children’s Minnesota clinic in downtown Minneapolis. “But they have come to accept that they need to do this, that their children need this, and it’s going to be okay.”

Between April and July, the hospital’s 12 clinics administered 8,324 vaccinations, more than triple the 2,562 given during the same period in 2016, according to hospital figures.

Earlier this month, a Somali American father whose children are immunized told Mackey he heard the same message from imams at five different mosques. Protect your child through vaccination, he recounted. The imams even offered to connect parents who had questions to the medical experts who could answer them, he said.

“I had never heard that before,” Mackey said. “I got the sense there was hope, that the tide was turning because of the faith leaders being involved.”

Doctors say they had tried without success to overcome the fear and misinformation that ­anti-vaccine groups have planted in the Somali American community for nearly a decade. That misinformation highlights the vaccine-autism claim, despite extensive research disproving any link.

Somali American children in Minnesota had a vaccination rate of 92 percent in 2004, higher than the state average, but the rate plummeted to 42 percent by 2014. During the measles outbreak, however, immunizations for those children, as well as for all others, have soared.

During the height of this year’s measles outbreak in Minnesota, vaccination rates for measles, mumps and rubella climbed dramatically. They remain at a higher level than before the outbreak began. (Minnesota Department of Health)

Measles, once a common occurrence, was eliminated in the United States in 2000. Experts say it has resurged in recent years, mainly because of the growing number of parents who refuse to vaccinate their children or delay those vaccinations.

Infection causes fever, runny nose, cough, red eyes, sore throat and a rash. The virus is usually cleared within 14 days, but it can cause serious, even deadly complications, including pneumonia, blindness and encephalitis, or swelling of the brain. One rare complication, for which there is no cure, kills children years after they have been infected.

Even with increased attention to the disease’s dangers, the anti-vaccine groups “definitely are upping their outreach on the political spectrum,” said Kris Ehresmann, director of the infectious diseases division for the Minnesota Department of Health. “I don’t think the outbreak slowed them down at all,” she said.

Earlier this summer, health officials and advocates received word that white women were passing out fliers and talking to families in some high-rise apartment buildings in predominantly Somali neighborhoods. The women reportedly claimed that the measles outbreak had been created by the Health Department to persuade Somali parents to vaccinate, said Lynn Bahta, a longtime state Health Department nurse who works to counter vaccine hesitancy.

Health officials never determined who the women were. But the reports reflect the tendency of anti-vaccine activists to “dig in,” Bahta said. “The more pressure on them, the more they dig in.”

The Minnesota Vaccine Freedom Coalition said in its Facebook post that its organizations “have not been aware or involved in” such targeted activity.

“That sort of thing would be completely outside of our mission,” the post added. “Unlike the department of health and many doctors, we don’t tell people what to do. We are about informed consent — sharing scientific data and Minnesota laws so citizens know THEY have choices and the right to make them.”

Alice Crites contributed to this report.