By Jeremy Ross

CHICAGO (CBS)– As Passover approaches, some synagogues will be putting signs up on doors warning unvaccinated congregants.

For Rabbi Ari Hart and Debbie Eisenstein of Skokie Valley Agudath Jacob synagogue, their place of worship is one demanding hundreds of visitors for the upcoming holiday have immunity to the ongoing measles outbreak.

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“If you wish to participate in our shul’s programing, whether that’s services or the open seder, which we’re hosting here tomorrow night which were hosting for folks across the area, you have to be vaccinated,” Heart said.

Dr. Bridget Wild of Evanston’s NorthShore University Health System supports the immunization demand.

Wild said the air that someone coughs or sneezes into, who has this virus, is spreading this virus is infectious for up to 2 hours afterwards.

She said people are able to spread the illness before they are symptomatic.

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“It’s scary,” Eisenstein said.

This on the heels, of New York City declaring a public health emergency. Since September in Brooklyn, more than 250 people have contact measles, mostly members of an ultra-orthodox Jewish community.

This disease can spread quickly in tight knit groups like those sharing a house of worship.

Rabbi Heart admits his new policy isn’t perfect.

“We’re not going to be checking every single individual who walks into the building immunization cards,  we don’t have the capacity to do that,” Hart said. “We welcome everyone but inclusion can’t come at the cost of safety.”

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According to the Centers For Disease and Prevention, there are 555 cases of measles so far this year and 372 cases all of last year.