BROOKLYN, N.Y. – New York City officials on Tuesday declared a public health emergency and ordered mandatory measles vaccinations to halt an outbreak concentrated among ultra-Orthodox Jews in Brooklyn, putting in place the broadest vaccination order in the United States in nearly three decades.

The order is the latest flashpoint in a nationwide battle to try to stop the second biggest flare-up of the disease since 2000 – spurred by travel to hot spots like Israel experiencing its own outbreak and widespread misinformation about vaccines that has frightened a generation of parents who have never witnessed the ravages of one of the most contagious diseases on Earth firsthand.

New York’s action comes as health officials scrambled to blunt the spread of measles, especially with the approach of Passover, a holiday associated with travel and big family gatherings, in what is the city’s largest outbreak since 1991.

New York’s mandatory vaccination order in four Brooklyn zip codes is by far the toughest action to date by state or local officials, as the disease’s tally grows to 465 cases in 19 states. Officials there and elsewhere have sought to bar unvaccinated children from schools and other public places but have had only limited success.

“We cannot allow this dangerous disease to make a comeback here in New York City,” Mayor Bill de Blasio, D, said Tuesday. “We have to stop it now.”

At least 285 people have contracted the disease in the city since September, mostly in Brooklyn’s Williamsburg neighborhood.City officials said Tuesday that 246 were children. Twenty-one have been hospitalized – five of those in the intensive care unit. There have been no deaths.

“This is the epicenter of a measles outbreak that is very, very troubling and must be dealt with immediately,” de Blasio said at a news conference. “The measles vaccine works. It is safe, it is effective, it is time-tested . . . The faster everyone heeds the order, the faster we can lift it.”

The mandate orders all unvaccinated people in four zip codes to receive inoculations, including children as young as 6 months old. Anyone who resists faces a misdemeanor charge and could be fined up to $1,000.

Officials said it will be enforced primarily by tracing the contacts of everyone diagnosed. The health department will investigate where each person has gone while contagious, and all the people they may have interacted with. If investigators find an unvaccinated child who could have been exposed to measles, that child’s parents could face a violation and be subject to fines, officials said.

One pediatrician in private practice in Williamsburg applauded the effort but feared it would be too little, too late to stop an epidemic.

“It’s a war zone,” said the doctor who said he had seen over a hundred patients who hadn’t been vaccinated but asked for anonymity for fear of jeopardizing his practices. “I think the city is underestimating the scale of the outbreak.”

But some in this insular ultra-Orthodox community expressed anger and suspicion, suggesting the city was conspiring with nefarious doctors.

“The doctors are trying to screw us, I’m sure of it,” said Bery Schmeltz, a 28-year-old yeshiva student, declining to say whether or not he was immunized. “The city is just trying to make money off us.”

There are no strictures against vaccines in the Jewish religion and the overwhelming majority of American Jews are vaccinated. The reasons for the explosion of cases among members of insular, ultra-orthodox communities has more to do with their frequent contacts with Israel, which is undergoing its own measles crisis, combined with their insularity and general mistrust of government, say health officials.

In addition, a misinformation campaign, including phone calls, voice mails and pamphlets has targeted the community, say health officials and immunization advocates. One widely distributed booklet not only cites various rabbis questioning the obligation to vaccinate children, but also advances anecdotes and statistics in an attempt to connect vaccinations to physical harm and death.

New York officials say that the outbreak in the ultra-Orthodox community began when individuals contracted the illness while visiting United Kingdom, the Ukraine, which has a huge outbreak and Israel, which also has a large outbreak.

Israel has no requirement that children be vaccinated before entering grade school. Although it has high overall vaccination rates, there are some groups with vaccine hesitancy, public health legal experts said.

The last time city public health officials relied on mandatory vaccinations also involved a religious community in a far more virulent measles outbreak that swept the country in 1991. In Philadelphia, health officials sought a court order to force parents at two congregations to vaccinate their children. The outbreak was centered in the Faith Tabernacle Congregation, which “did not believe in either immunizations or medical care,” according to Robert Ross, in a 2015 interview with National Public Radio.

Ross, who was deputy health commissioner at the time, said the church ran a school with about 1,000 children, none of whom were vaccinated.

By the time the vaccines were administered, the measles outbreak in Philadelphia was subsiding – after nine children had died, including six from Faith Tabernacle.

In the United States, courts have supported officials in overriding individual rights to protect public health, said Dorit Reiss, professor at U.C. Hastings College of Law in San Francisco.

The New York City health code is also “very, very broad and gives [officials] extensive authority,” she said. Under the code, the health commissioner has the authority to declare public health emergencies and take reasonable action “necessary for the health and safety” to protect against an existing threat.

Michelle Mello, a professor of law and health research and policy at Stanford University, said the $1,000 fine was a relatively low penalty and the order may be more symbolic.

“If you’re a hard-core anti-vax believer, a misdemeanor conviction and a $1,000 fine is not going to change your mind,” she said. But for many others who haven’t yet gotten their children immunized, this may prove decisive, she said.

The city’s health commissioner, Oxiris Barbot, said New York’s outbreak “is being fueled by a small group of anti-vaxxers in these neighborhoods.” In a statement earlier this week, she added: “They have been spreading dangerous misinformation based on fake science.

City officials said that insured adults and children will be covered. Those who are uninsured will pay what they can afford, de Blasio said, and those who cannot afford the vaccination will receive it free.