An unfounded fear of vaccines has spread around the world in recent years, with childhood vaccination rates reportedly declining in several countries as a result. Nothing in the belief system of Orthodox Jews makes them any more likely to oppose vaccines, and several Orthodox rabbinical organizations have called on parents to vaccinate their children. But Hasidic Jews are prey to the same misinformation that has affected others, and some ultra-Orthodox rabbis have come out against vaccines.

Mr. Wieder, who said he first learned about the order in news reports, felt that the exclusion of the Hasidim from the decision-making process was emblematic of the divisions in the county and would only sow more mistrust. “When you have people who are true haters,” he said, “they will take advantage of this type of situation and it just pours fuel on the fire.”

Steve Gold, the chairman of the Jewish Community Relations Council for the Jewish Federation of Rockland , shared Mr. Wieder’s concerns, saying the move by county officials risked exacerbating the anti-Semitism that already existed in the area before the measles crisis. He pointed to a number of anti-Semitic episodes, including swastikas spray-painted on trees.

“I think it just opened up the door for everybody to say whatever they wanted to say,” Mr. Gold said. “And they’re putting, the way it looks right now, 100 percent blame on the Orthodox community. ”

The anxiety over the outbreak has spread from the aisles at the kosher supermarkets where women in head-coverings pushed shopping carts laden with babies and goods for the coming Passover holiday, to the ritual bathhouses or mikvahs. In children’s clothing shops, mothers buying Sabbath finery traded stories about friends with sickened children.

Near a strip mall that sold religious candelabra and fur hats, a group of teenage boys tugged at the prayer threads that hung at their waists, discussing whether they would hang out with unvaccinated friends.

Robin Goldstein, a Hasidic mother and a social worker, said that some in the community viewed the county orders as governmental overreach into their decisions not to vaccinate, which has left them no choice but to comply.