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For months, New York City officials have been fighting a measles outbreak in ultra-Orthodox Jewish communities in Brooklyn, knowing that the solution — the measles vaccine — was not reaching its target audience.

They tried education and outreach, working with rabbis and distributing thousands of fliers to encourage parents to vaccinate their children. They also tried harsher measures, like a ban on unvaccinated students from going to school.

But with measles cases still on the rise and an anti-vaccination movement spreading, city health officials on Tuesday took a more drastic step to stem one of the largest measles outbreaks in decades.

Mayor Bill de Blasio declared a public health emergency that would require unvaccinated individuals living in Williamsburg, Brooklyn, to receive the measles vaccine. The mayor said the city would issue violations and possibly fines of $1,000 for those who did not comply.