They came in a steady stream to a synagogue community center in the suburbs of Detroit: firefighters in uniform, mothers pushing strollers, men in dark suits, local workers on their lunch break. They passed through doors emblazoned with a warning: “This clinic is for vaccinations only. Do NOT enter if you have any symptoms.”

Inside, a team of health workers passed out clipboards and prepped people for shots to protect them against the country’s latest outbreak of measles—a disease that was all but eliminated two decades ago but that is making a potentially deadly comeback fueled by international travelers and homegrown anti-vaxxers.

“It’s beyond my comprehension why people would choose not to vaccinate,” said Lisa Shevin, a grandmother of two baby boys, ages 4 months and 7 months, who live in Oak Park, Michigan, an Orthodox Jewish enclave that is the epicenter of the outbreak.

Shevin said her daughter, afraid her infant son may get infected, has become a virtual shut-in since the news that an Israeli traveler had brought measles to the community and that it was spreading fast. She said she was nervous after learning the kosher grocery store where her son works was listed as a possible infection site. “He went and got the booster,” she said, “so he’s good.”

More than 1,400 people have rushed to three free makeshift clinics to get vaccines or boosters since the outbreak was announced. Among them, at Young Israel of Oak Park, was Cindy Starman, a 62-year-old who works with special needs children, and decided to get a booster.

“You know what? Better safe than sorry,” she said. “I mean, nobody wants measles.”

As of Thursday afternoon, Michigan officials had confirmed 22 measles cases, all but one in Oakland County. The outbreak is already the state’s worst in more than two decades, and is likely to keep growing.

“At this point it’s in the community,” said Leigh-Anne Stafford, Oakland County health officer. “We know measles is a very contagious disease.”

Metro Detroit is a hotspot for the anti-vaccination movement, according to a 2018 study in PLOS Medicine. Largely affluent Oakland County ranked fifth nationally among counties for the number of kindergartners who receive non-medical exemptions. The county has also seen bitter court battles between parents who disagreed about vaccinating their kids; in 2017, one anti-vax Oakland resident served jail time after refusing to comply with a judge’s orders to get her 9-year-old son immunized.

One of the people who showed up at the Young Israel clinic this week was a 26-year-old woman anxious about the health of her 5-month-old, and who wanted her Azerbaijani nanny to get a shot.

“I’m worried, but I’m trying to take whatever precautions I can,” she said.

Asked by a reporter if she knew any anti-vaxxers, the young mother promptly called a friend, who began arguing her position. “K, I don’t want to get into this debate now,” the mom responded. The friend declined to speak to a reporter, explaining that since the outbreak began, she and other local anti-vaxxers feel under attack.

Health officials in the Pacific Northwest, where more than 70 people have been diagnosed with measles in Oregon and Washington, have blamed the increasingly organized anti-vax movement for the stubborn outbreak.

In Rockland County, New York, where 150 people have been sickened, officials this week declared a state of emergency banning unvaccinated children from public places—a measure that appeared to be toothless but that underscored the desperation of public health officials.

Authorities also publicly shamed several New York City yeshivas for flouting a ban on unvaccinated children as an outbreak that began in October has infected for more than 200 people.

In Michigan, the Orthodox community, including religious leaders, appears to be mobilizing to fight the virus. Last week, the Council of Orthodox Rabbis of Greater Detroit issued a statement that Jews were “halacichally obligated” to help prevent the spread of disease and should follow Michigan Department of Health vaccination guidelines. Detroit Hatzalah, an Oak Park-based emergency medical volunteer organization, set up a measles hotline and has been sending ambulances in response to potential infection calls, which avoids the nightmare scenario of a contagious person showing up to a doctor’s waiting room, where the virus can live for up to two hours.

“People are definitely concerned,” said Rabbi Robert Gamer, of Congregation Beth Shalom, a Conservative synagogue in Oak Park. He said the vast majority of congregants are immunized, and some have been asking him for his religious interpretation of the debate.

There are rare medical exceptions, he answers. “Other than that, “I’ve never seen anything in Jewish law that would say that you shouldn’t be vaccinated.”

Health officials believe the Israeli traveler probably contracted measles during a visit to New York before coming to Oakland County, where it spread quickly because the community is dense and tight-knit, with many residents frequenting the same schools, synagogues, and shops. On March 14, the first day the virus was present in the area, according to a county health department list, three synagogues and a yeshiva were potential exposure sites. Within a week the list had expanded to some 80 locations, including kosher markets, bakeries, multiple hospitals and urgent care centers, a car wash, Walgreens, Home Depot, and 7-Eleven.

While some new mothers may be avoiding public places with their babies, daily life in Oak Park seemed largely unchanged this week. A strip mall with kosher delis and markets was busy; across the street from Young Israel, at a yeshiva, boys played soccer on an enclosed field, not far from a big measles warning plastered on the school’s front door.

Friends and family gathered for Purim last week. At Beth Shalom, which held a children’s carnival ahead of evening prayers, Shevin’s grandson came dressed as a devil. The event was well-attended. “At that point we didn’t know the full extent of how much further it was going to keep going.”

The confirmed cases are in people ages 11 to 63. One Oak Park man, Avi Cohen, 23, got it even though he was vaccinated as a child. (Health officials say vaccines don’t work for roughly 3 percent of the population.)

After developing a bad cough and fever, Cohen, a father of two young children and teacher at a nearby Hebrew day school, went to the hospital, where doctors told him he had an upper respiratory virus and released him. Cohen developed a rash, and several days later, after visits from both Hatzalah and state health officials, he tested positive for measles.

The rest of his family is vaccinated—and was vigilant even before he fell ill. When the family learned Cohen’s 2-year-old son had been in a synagogue listed as a possible exposure site, his parents took him to get a swab test, which came back negative, and still took the kids to stay with grandparents.

“You do what you can,” Ita Leigh Cohen, Avi’s mother, told The Daily Beast. “And then the rest is not in our hands.”