Noah Abdullah hasn’t immunized his 4-year-old son, Michael, saying that he’d read vaccines might be “no good” and that he’d “rather do natural things” to strengthen his child’s immune system.

“I need to see more information before I start shooting him up with stuff,” Mr. Abdullah said.

Donna Mosley said her 3-year-old grandson also did not have his vaccinations, though she wishes he did. His mother is afraid the shots could cause autism, she said, and his father’s Muslim beliefs have made him “totally against it.”

The two boys attend Sister Clara Muhammad Elementary School in Harlem, a small school where most children had a religious exemption to immunization in the last school year, according to city health department data.

As the measles outbreak deepens in New York City, health authorities have been focusing on schools affiliated with ultra-Orthodox Judaism, because those are the only city schools within which measles transmission has occurred so far. But immunization data, reported annually by every school to the state, suggests that reluctance to vaccinate in New York is much more widespread.

The majority of the dozens of New York City schools that had less than 90 percent of their children vaccinated for measles in the last school year were not ultra-Orthodox Jewish, according to the data, which is reported by the schools themselves.

Several were Muslim schools, while others were Bible-centered Christian academies. Some were schools that hew to nontraditional philosophies, including the Waldorf education movement, which tends to attract parents who favor alternative medical practices. Some served autistic or special-needs children.

Because the schools’ immunization data is self-reported in mid-December of each school year, it offers only a snapshot that can change as students are vaccinated. But the data can serve as a guide for finding pockets of vaccine reluctance that was borne out in interviews with parents.

Vaccines have been proven to be safe and effective against the spread of disease, and there is no evidence that they cause autism.

For now, the ban on unvaccinated children attending school in New York City applies only to children who attend Orthodox Jewish schools in the four most affected ZIP codes in and around Williamsburg, Brooklyn, the center of the outbreak.

There were 31 new cases in Williamsburg last week, bringing the total measles cases in the city since September to 466.

If the outbreak reaches beyond the Orthodox Jewish community in Brooklyn, as public health experts fear, other schools with low vaccination rates could also become hotbeds for the disease.

In a worrying sign, two cases of measles reported this week occurred in students with religious exemptions who attend public schools in Sunset Park, Brooklyn.

Dr. Oxiris Barbot, the city health commissioner, said Tuesday that both of the children had spent time in a part of Brooklyn with measles activity, and were not in school while they were contagious. She urged people to remain calm and get vaccinated.

Daniel Salmon, the director of the Johns Hopkins Institute for Vaccine Safety, said that the clusters of parents who are refusing vaccines, in New York and elsewhere, were making him worry that the measles outbreak could turn into a measles epidemic.

“The story with measles for the past 20 years is that it starts among refusers, it spreads predominately among refusers, and along the way it picks off other kids,” he said. “Up until now, we have been able to put a stop to it. But I’m nervous. I’m afraid what happened in Europe is going to happen in the U.S.”

Sister Clara Muhammad in Harlem is part of an Islamic school system affiliated with Warith Deen Mohammed, who transformed the original Nation of Islam movement into an African-American-centered Sunni Muslim community in the 1970s.

The tiny school is on the upper two floors of the Malcolm Shabazz Mosque in Harlem, on a site where Malcolm X preached. Eleven students are enrolled this year, state data showed, and last year, two of the three enrolled students had religious exemptions.

Mr. Abdullah, 38, the parent at the school who is reluctant to immunize his 4-year-old son, Michael, said he was concerned about the measles outbreak and would seek out more advice.

“I was going to talk to his doctor at the next visit to find out what’s going on,” he said.

The modern-day Nation of Islam movement has been outspoken about its anti-vaccine beliefs, but less is known about patterns of vaccine refusal in Sister Clara Muhammad schools around the country. The school’s administration did not respond to a request for comment. Read more at NY Times