(CNN) - As one of the holiest Jewish celebrations of the year arrives, families in the Hasidic section of Williamsburg, Brooklyn, face a dilemma.
"Say you have six kids that want to come to the Seder, with all the grandchildren," said Eli Banash, 32, a member of the Orthodox community who works in Williamsburg.
"Grandmother wants everybody to come. One family didn't vaccinate the kids. Five did. The five families are saying, 'We're not coming unless they don't come!' With Passover, it's going to intensify."
A persistent measles outbreak has hit this ultra-Orthodox enclave and led city officials to declare a public health emergency.
Passover, which begins at sundown Friday and ends April 27, marks the Exodus story from the Bible and is celebrated with large gatherings and ceremonial meals. But community leaders and health officials fear the holiday may further fuel the spread of the highly contagious disease.
Already, 359 cases of measles have been confirmed in Brooklyn and Queens since October, mostly in Williamsburg. The outbreak began when, according to health officials, an unvaccinated child became infected with the illness while visiting Israel.
"The concern is that with Passover and increased travel, we're going to be putting more people at risk," said New York City's health commissioner, Dr. Oxiris Barbot.
Across the country, measles cases have jumped to the second-highest level in a quarter century, with 555 cases confirmed in 20 states, according to the US Centers for Disease Control and Prevention.
"Because of measles' long incubation period, we know this outbreak will get worse before it gets better," Barbot said in a statement this week.
A pamphlet directed at Orthodox communities helped fuel the fear of vaccines
In Hasidic Williamsburg, bearded men walk hurriedly in long frock coats crowned by black hats. Women in ankle-length skirts push strollers on crowded sidewalks and Hasidic boys with spiraling side curls dart through the streets in bunches.
In an insular community where some don't take kindly to intrusion, residents blame the outbreak largely on a hardline minority opposed to vaccinations, or anti-vaxers. The close-knit neighborhood -- where residents explain the insularity as a way of preserving the community's identity -- has seen heightened tension in some families, especially as Passover preparations got underway.
Blima Marcus, a nurse and past president of the Orthodox Jewish Nurses Association, has been holding small workshops with the nurses in Brooklyn and New Jersey to educate members of the ultra-Orthodox community who are fearful of vaccines.
The fears were fueled in part by a slick 40-page booklet being distributed in Orthodox enclaves about the dangers of vaccines. The booklet is directly aimed at the Orthodox community, partly written in Hebrew and filled with snippets from the Torah. Yet Marcus and Orthodox Jewish leaders say there is nothing in Jewish law that prohibits vaccinations.
The booklet was created by a group called PEACH, or Parents Educating and Advocating for Children's Health. Attempts to reach the organization for comment have been unsuccessful.
"People figured it's a fringe magazine and didn't pay a lot of attention to it, but I think what we're realizing now is that it had a much larger impact than anyone ever realized," Marcus said.
'Every night, people are arguing'
Burach Kahan, 25, said he had his youngest child, 9 months old, vaccinated this week. His two other children are vaccinated. He said he started a separate family text group where most of his 13 siblings can only talk about vaccines and the measles outbreak.
"One of my sisters is very scared," he said. "Most of her friends are anti-vaccine and she forwards all their messages. She brought (up vaccines) on the regular group and everyone was busy all day and night fighting."
"People will argue throughout the holiday," said Shaya Hershko, 22, who had his 14-month-old daughter vaccinated against the measles before a family Passover trip to Canada. "Every night, people are arguing. The people you argue with about everything -- your arguing partners."
Hershko, who lives in Williamsburg, frequently argues with his sister-in-law in upstate Orange County, New York. He says she is an adherent of alternative medicine and refuses to vaccinate her children.
Orange County had seen 20 confirmed measles cases, while neighboring Rockland County -- with 190 cases -- tried to bar unvaccinated children from public places until a judge prohibited officials from enforcing that rule.
"I have a lot of friends that didn't want to give the shots but I figured that a doctor knows better than my friends know," said Hershko's wife, Friny, 20. "The people that don't give the shots are actually a little bit looked down because the schools and everybody are making like a big deal."
New York health officials announced last week that in the neighborhoods affected by the outbreak, anyone who has not been vaccinated against measles or cannot show evidence of immunity could face a $1,000 fine.
Nurses are fighting misinformation
On Monday, the health department said a Williamsburg child-care program was closed "for repeatedly failing to provide access to medical and attendance records." Schools and child care programs are required to maintain records on-site, and unvaccinated students and staff are prohibited from attending.
The child care program has reopened, but health officials said Thursday that four other city schools and pre-schools will close imminently for failing to comply with the department orders.
Marcus and a group of other nurses have researched and refuted each piece of misinformation in the PEACH booklet, and plan to soon publish a rebuttal to be distributed in Orthodox communities.
The nurses have also been meeting with mothers in Williamsburg and other Orthodox communities, Marcus said.
"I feel really bad for these women whose internal instincts of motherhood and protecting their children have been exploited by this movement and now are feeling that heat and feeling that backlash and are being kind of attacked for their medical choices," she said.
"I talk to these women and I say you're trying to use Jewish law to defend not vaccinating. Instead, you're deliberately trying to harm them. It's almost kind of like breaking your child's bone in the hope that when it grows back it will be stronger," she said.
"We listen to them and take them seriously on an issue where they're usually mocked," Marcus said.
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