As New York City's largest measles outbreak since 1991 worsens, Mayor Bill De Blasio on Tuesday declared a public health emergency mandating that any unvaccinated children living in certain ZIP codes must receive the measles-mumps-rubella vaccine or their family could face heavy penalties.

Just days after a judge threw out Rockland County's emergency order to ban unvaccinated kids from all public places, NYC's Deputy Mayor for Health and Human Services Herminia Palacio has, with the mayor's approval, declared a state of emergency as the number of measles cases since the fall nears 300, with 21 cases resulting in hospitalizations, and nearly 250 in children.

Palacio blamed anti-vaxxers for spreading false information among Brooklyn's Hasidic Jewish community, which has been identified as the epicenter of the outbreak, per the WSJ:

Public health officials said they were taking the unusual step in response to an antivaccination campaign that has included measles parties, phone calls and voice mails targeting the community with “intentional efforts to give misinformation,” said Herminia Palacio, New York City’s deputy mayor for Health and Human Services. "There are frank untruths being propagated," said Dr. Palacio. The emergency order covers ZIP Codes 11205, 11206, 11211 and 11249.

City officials will be checking medical records to try and track down children who haven't been vaccinated.

Officials with the city’s Department of Health and Mental Hygiene will be checking vaccination records and tracking down adults and children who have been in contact with infected patients. People who have not received the MMR vaccine, or don’t have evidence of immunity, could be fined $1,000. City officials said on Tuesday that there have been 285 cases of measles in New York City since October, with 246 cases in children. Twenty-one people have been hospitalized, with five ending up in the intensive care unit, but there have been no deaths. Some children younger than 6 months—who are too young to receive an initial dose of the MMR vaccine—have been exposed to measles. Nearly all cases have been in the Orthodox community, according to New York City Health Commissioner Oxiris Barbot.

According to the New York Times, across the country, there have been 465 measles cases since the start of 2019, with 78 new cases in the last week alone. New York and New Jersey have accounted for more than half of these.