She now felt certain that her third child’s speech and hearing delays had worsened after he started getting vaccines. She reached out to a well-known vaccine skeptic named Mayer Eisenstein. Unlike her own pediatrician, Eisenstein listened sympathetically to her concerns and even gave her his cell phone number. By the time Chany’s fifth child was due to receive shots, she was firm in her convictions. She believed vaccination had caused her children’s disabilities. “I realized it was my mistake,” she says. “And if I made a mistake, I’m going to have to fix it.”

Chany decided to create a forum for women in her community. “No one likes to be alone,” she says. “If your child just got a vaccine and now he doesn’t speak anymore, your doctor’s not going to answer that.” Since some Hasidic sects frown on internet use, ultra-­Orthodox women often receive community news, inspirational talks, and other information by way of the phone. Chany worked with others who set up a hotline called Akeres Habayis, or Woman of the House, so that she could use it to share information. “Mothers can feel when something’s wrong with a child,” she told me, “and you should listen to their feelings and not disrespect them.”

This sense of being disrespected and dismissed by doctors fueled Chany’s distrust of vaccines, but her suspicion of medical authorities may have had deeper roots. Two of her grandparents were survivors of Auschwitz. The other two lived in Romania under communist rule, where they were subjected to physical violence, before coming to Brooklyn in the 1960s. Torture, medical experimentation, and death by government edict seemed an inescapable part of Chany’s inheritance, and it was one she shared with members of her community. She viewed efforts by secular health departments to mandate vaccination as a threatening intrusion on private life.

Chany began to host conference calls, later posted on Akeres Habayis. She began inviting guest speakers, including well-known vaccine skeptics. One of her first guests was Mayer Eisenstein, and 47 people called in. Some of the most popular calls drew several hundred women to live conversations, with a thousand or more dialing in later to listen to the recordings. Chany got to know a wide range of antivaxxers who had risen to prominence on the internet but had not yet found a foothold among the ultra-Orthodox. The hotline made her a powerful conduit of misinformation into a world that often shunned outsiders.

As Chany cultivated ties with other like-minded ­people in her community, she came up with an informal name for the network: Peach (Parents Educating and Advocating for Children’s Health). “It was just a name,” she says. “It was a way to identify people who were in the same situation.” Around 2012 or 2013, a man named Moishe Kahan reached out to her about collaborating. Kahan lived in Williamsburg, another Brooklyn neighborhood with a large ultra-­Orthodox community. Kahan had grown up in London and hadn’t had vaccines as a child. Over time he became fiercely resistant to the very idea of them. Kahan developed a presence on Facebook, promoting conspiracy theories from sources like Infowars. He also became an independent distributor for a company called Immunotec, which sells dietary supplements and has funded research on the use of its products for children with autism. (Kahan did not respond to emails requesting comment.)

Chany and Kahan joined forces. In 2014, Peach released a pamphlet called “The Vaccine Safety Handbook: An Informed Parent’s Guide,” listing Kahan as a contributing researcher. It was paid for by advertisements from local businesses and was filled with tales ostensibly linking vaccines to autism, SIDS, allergies, asthma, and cancer. A series of illustrations shows mothers struggling to communicate with arrogant doctors. “Doctor, my child became autistic/epileptic/anaphylactic after his vaccines,” says one woman, cradling an infant in her arms. “Obviously your child was defective. Vaccines are perfect,” the doctor replies. “How many ‘defective’ children would have remained perfectly healthy if not for vaccines?” asks the caption.

In another illustration, a woman stands with her arm around a small boy. “My son regressed into autism after his MMR vaccine. Now he’s in his own world and can’t communicate,” she says. “But at least we had no problem enrolling him in school.”

The tone of bitterness and regret in the handbook mirrored Chany’s feelings. So, too, did the call to mothers to feel empowered. There was an email address people could write to, and Chany would respond. The pamphlet also provided the number for a “Peach Hotline,” which connected callers to Akeres Habayis. Through the hotline they solicited volunteers, and Chany told those who contacted her how to distribute the pamphlet in their neighborhoods. “It’s a grassroots movement,” she says. “It’s literally person to person.”

In early 2014, an ultra-Orthodox woman named Zahava, who lives in Williamsburg, found a copy of the Peach pamphlet on her doorstep. For more than 70 years, Williamsburg has been home to Hasidic Jews, many descended from Eastern Europeans who settled there after surviving the Holocaust. Hasidim tend to live in close communities, living by tenets set forth in Jewish texts. Zahava, who agreed to speak as long as her full name wasn’t used, is devout and lives in a large apartment building, where children play together and extended families gather for meals. Others in her building received the Peach pamphlet too, and friends and neighbors pored over the sensational claims, especially those about autism.

Roughly 40,000 copies of the pamphlet appeared in kosher grocery stores and by apartment doors in Williamsburg and Borough Park, as well as in ultra-­Orthodox communities in upstate New York and New Jersey. Zahava, who has delicate features, pale skin, and light eyes, read the pamphlet just months after giving birth to her first son. She felt terrified. The pamphlet played on the anxiety that she and other new parents often feel about bringing babies into a world of pesticides, plastics, and pollutants, and it seemed to offer a simple explanation for virtually any physical or developmental anomaly. “It doesn’t take much to put fear into a mother,” Zahava says. “And once the fear is there, it is very hard to get out of it and go to the logic.”

Zahava did her shopping at an upscale kosher market and had the groceries delivered to her home. One day, inside her order was another copy of the pamphlet. It came again with subsequent food deliveries, filling her with dread about vaccinating her infant son. Each time she took her boy for a checkup or sick visit, she bombarded Dov Landa, the physician assistant who treated her child, with questions. She felt reassured by his well-­informed answers and his concern for her son, but the self-doubt would creep back in.

One day at the grocery store, Zahava saw a pile of the pamphlets and felt her distress well up again. After asking the cashier if she could have them, she walked out with the stack and dropped it into the nearest trash can. Eventually, after her husband consulted with a rabbi, who assured them that the shots were safe, Zahava brought her son to Landa for his vaccinations.