“Minke” used to get her kids vaccinated, though she never felt right about it. The thought of injecting her children with a foreign substance — one that might cause them to run a fever or have an allergic reaction — scared her, even if it might protect them from measles, polio and other life-threatening diseases.

But three years ago, when her youngest daughter’s pediatrician said it was time for a chickenpox shot, she balked. After all, kids get chickenpox all the time, she thought.

That’s when Minke became an anti-vaxxer.

About 9% of Americans think vaccines are not safe, but Minke is unusual even among that vocal minority. She is an ultra-Orthodox Jew, part of a community known for adherence to the rulings of their rebbes — rabbinic leaders. And many of those rebbes have insisted that Jewish law requires vaccination. But a stubborn, if small, segment of the ultra-Orthodox community is saying that, when it comes to vaccines, their rebbes’ decrees do not apply.

“I believe that there is no Torah source to tell me exactly how to take care of my children,” Minke, 31, said in an interview. Minke requested a pseudonym because she did not feel comfortable having her views publicly known.

It is very unusual for Hasidic Jews to go against the prevailing ultra-Orthodox interpretation of Jewish law, said Rabbi Yair Hoffman, a Hasidic educator and commentator who writes frequently about Jewish legal decisions.

“They’ve [the anti-vaccine cohort] been convinced by people that the rabbis have made an error, and are really relying on a minority view instead of a majority view,” Hoffman said.

Hoffman said he knows of only one other instance of Hasidic Jews going against the majority of rabbis’ legal opinions. There is a segment of women in the community who eat and drink on the four minor fast days in the Jewish calendar — despite the fact that virtually all rabbis agree that fasting is required by Jewish law for both men and women.

Measles is a highly contagious disease that spreads through the air. It can be fatal in rare cases, but also poses significant health risks by lowering the body’s ability to defend itself from infections for up to two years after the infection, according to Dr. Jennifer Lighter, a pediatric epidemiologist with the New York University Langone hospital system. The diseases was considered eradicated in the U.S. in 2000, meaning that there are only limited outbreaks, and no continuous transmission of the disease.

The American ultra-Orthodox community of about 300,000 people has seen multiple measles outbreaks over the years due to low vaccination rates. The current outbreak in New York, in ultra-Orthodox enclaves in Brooklyn and the Hudson Valley, has caused over 170 ultra-Orthodox Jews to be infected.

Some major rabbis have said it’s okay not to vaccinate children before sending them to school, including three members of the top rabbinical council of Agudath Israel of America, the leading ultra-Orthodox umbrella organization. The three rabbis signed onto a letter that stated that any parent who “done his research” is allowed to go against the advice of the medical establishment. One of those rabbis called vaccines a “hoax” in a 2014 interview. Smaller yeshivas, or religious schools, are not as stringent about excluding unvaccinated kids as the larger ones, said Samuel Heilman, a professor of sociology at Queens College who has written extensively about the ultra-Orthodox community.

In some yeshivas in upstate New York, vaccination rates are as low as 60%, according to New York state health commissioner Dr. Howard Zucker. New York state’s overall vaccination rate is 92.5%.

Yet most major ultra-Orthodox rabbis and institutions have insisted on vaccination. Two of the largest yeshivas in the world — the Beth Medrash Gevoha in Lakewood, New Jersey, and the Mir Yeshiva in Jerusalem — have both stated that their thousands of students and teachers are required to get vaccinated. Ultra-Orthodox authorities on Jewish law have argued that the Talmudic imperative of pikuach nefesh, or saving a life, stipulates that all should be vaccinated to prevent the wider community.

Heilman says the leading rabbis could do more: “Frankly, the rabbis could put a stop to this overnight if they simply said, ‘Anyone in whose family there is no vaccination can’t go to yeshiva.’ Because these kids can’t not go to yeshiva.”

Minke said that, in her social circle, vaccine skepticism is growing. People feel unfairly targeted for vaccination by the city and state departments of health. They are taking their intuition that vaccines are dangerous, she says, and then learning on the internet about, for example, the erroneous anti-vaxxer belief that vaccines routinely cause autism and other conditions.

Minke, a member of the Vizhnitz branch of Hasidic Judaism, considers herself as a “very strong conformer,” who listens to her rebbe. But she insists that the decision of whether or not to vaccinate is different, and should be made on “an individual basis.”

Other ultra-Orthodox anti-vaxxers say that the rabbis have not been given “both sides” of the vaccine argument, or have been bullied into siding with the medical establishment by major stakeholders in the community. National and international health organizations have repeatedly determined that vaccines are safe, and that adverse reactions are rare.

“All humans are fallible, even rabbis,” Yael Tusk, a 35-year-old Chinese medicine practitioner in Jerusalem who identifies as Orthodox, wrote in an email. “Is it realistic to expect that a halachic [legal] ruling that may be made in error cannot cause harm? I am not willing to take such a risk on my children’s health and lives.”

Opposition to vaccines may be growing in the ultra-Orthodox world as a response to the community’s perception that the secular world is trying to weaken their social structures, Heilman and others said.

“Usually people are alone, and they can’t fight a system alone,” said a Hasidic doctor of osteopathic medicine, who is board certified in Pennsylvania. The physician, who is opposed to vaccination, asked to be anonymous to protect his personal and professional reputation. “In the community, people are together, and they can withstand enormous pressure from the system, when they feel the system is saying to do something that is not in their kid’s best interest.”

At the same time, experts agree that the ultra-Orthodox world’s anti-vaccine crowd is a fraction of the community.

“You’re never going to get one hundred percent uniformity on anything,” said Ezra Friedlander, a Hasidic political consultant whose father is the rebbe of the Liska branch of Hasidic Judaism. “Moses couldn’t get that, and he split the sea.”

Update, 1/29/19 — This article has been updated with additional information about vaccines.

Ari Feldman is a staff writer at the Forward. Contact him at feldman@forward.com or follow him on Twitter @aefeldman