Amid a measles outbreak that first began when an unvaccinated child got the disease while visiting Israel, New York City has told yeshivahs in the Brooklyn section of Williamsburg that students must be vaccinated or else face violations or closure.

“Any school out of compliance will immediately be issued a violation,” the health department said in a release on Monday.

On Tuesday, Mayor Bill de Blasio declared a public health emergency.

“There’s no question that vaccines are safe, effective and life-saving,” he said. “I urge everyone, especially those in affected areas, to get their MMR vaccines to protect their children, families and communities.”

Since October, 285 cases of measles have been reported in Brooklyn and Queens with most of them involving Orthodox Jews.

Measles consists of runny nose, sore throat, rashes, red eyes and tiny white bumps in the mouth, according to WebMD.

In a statement by the city’s health department, Brooklyn Rabbi David Niederman said, “It says in the Torah ‘V’nishmartem Meod L’nafshoseichem’—a person must guard their health.”