"When you make the decision not to vaccinate your child, please understand you're also making that decision for the people around your child", warned Palacio, who said her services had received reports of so-called "measles parties" held to purposely expose children to the disease.
"We don't take any of this lightly", said the mayor, above a slogan telling people not to wait to get vaccinated.
"If people get involved quickly, no one will have to pay the penalty", said de Blasio.
The nation's biggest city is in the midst of its biggest measles outbreak since 1991, with 285 cases diagnosed since last fall - compared to two in all of 2017, officials said. Newborns, pregnant individuals, and those with weakened immune systems can not get vaccinated, so it is important that everyone around them be vaccinated in order to protect them from contracting the virus and prevent severe complications in these susceptible populations. It covers people who live in four ZIP codes in Brooklyn's Williamsburg neighbourhood, where more than 250 people have gotten measles since September. It is safe, it is effective, it is time-tested. Parents of children older than six months must get them vaccinated or show proof of immunization.
The outbreak began when an unvaccinated child visited Israel, where thousands of people have been sick, contracted the disease, and came back to Brooklyn.
The resurgence of the once-eradicated, highly-contagious disease is linked to a growing anti-vaccine movement in richer nations - which the World Health Organization has identified as a major global health threat.
City Hall declared a state of emergency Tuesday as it contends with a recent outbreak of measles centered in Brooklyn.
This follows an order in Rockland County that barred unvaccinated children from public spaces for 30 days. 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.
There have been 285 cases of the disease in Brooklyn and Queens since October, a lot of them involving members of the ultra-Orthodox Jewish community.
In a similar directive late a year ago amid an outbreak, the city ordered schools and child-care centers to keep unvaccinated students out of school. A court halted it last week, but County Executive Ed Day said Tuesday he planned to appeal.
Miranda said there's no blueprint for how city officials could forcibly vaccinate people. But you don't need to go as far as Madagascar - common tourist destinations like England, France, Italy and Greece had measles outbreaks a year ago.
He said Rockland officials are crafting a new order created to isolate people exposed to measles. Cases have been reported in Florida, Indiana, Massachusetts, Nevada, Arizona, California, Colorado, Connecticut, Georgia, Illinois, Kentucky, Michigan, Missouri, New Hampshire, New Jersey, New York, Oregon, Texas and Washington.