NEW YORK CITY (WPVI) -- Two areas of New York battling a growing measles outbreak.
And there are concerns that travelers and family gatherings during the Easter and Passover holidays could spread it further across the country.
Health officials in Michigan already believe their 49 cases are linked to an infected traveler from New York.
New York City mayor Bill de Blasio sent a serious message today. And another county in New York is enforcing stricter rules.
"We cannot allow this dangerous disease to make a comeback again here in NYC," said de Blasio at a news conference.
He declared a public health emergency for Williamsburg, a neighborhood in Brooklyn now with 285 cases of measles, mostly within the Orthodox Jewish community.
In 2017, there were just two cases of measles reported in all of New York City.
Measles isn't just a rash. It can cause serious illness, even death.
Vaccination is the best protection. It's now mandatory in Williamsburg for all unvaccinated people.
"It's crucial for people to understand, the measles vaccine works. it is safe, its effective, it is time-tested," de Blasio said.
The C-D-C is reporting a 465 confirmed cases in 19 states, including Brooklyn and Rockland County, just outside New York City.
Both are taking strong action to get the outbreaks under control.
Rockland County has 168 cases and has already declared a health emergency. Today, it announced extra steps to stop the outbreak.
Anyone exposed to measles will be ordered to stay home for 21 days. Violators there will be fined.
"One person with this disease can spread this exponentially," said Rockland County executive Ed Day.
In Williamsburg, violators also faces fines up to a $1,000 for anyone unvaccinated.
Schools not in compliance could also be shut down.
It's an effort to protect the entire community including people who can't be vaccinated and are at a greater risk.
"Such as infants, pregnant women, cancer patients on chemotherapy and other patients with weakened immune systems," says Dr. Herminia Palacio, New York City Health & Human Services director.
Even though this is going on in New York, it's important for people here to be aware.
NYC declares public health emergency in epicenter of measles outbreak
Officials concerned holidays could spread outbreak beyond city