The state of emergency in Rockland county, which comes into effect at midnight on Tuesday, bars anyone under 18 who is not vaccinated against measles from public places for 30 days.
"We must not allow this outbreak to continue indefinitely", County Executive Ed Day said in a statement announcing the emergency declaration.
The county is now experiencing its longest outbreak since 2000, with most of the cases involving members of the Orthodox Jewish community. "However, parents will be held accountable if they're found to be in violation of this emergency declaration".
More than 82 percent of the measles patients had not received a single dose of the MMR vaccine, health officials said.
"Every new case is a roll of the dice" that could lead to life-threatening complications, Day said.
The New York and Washington outbreaks began after USA travelers picked up measles in foreign countries, where the disease was running rampant, and brought it back to places where vaccination rates were too low by us public health standards.
This month, a federal judge, citing the "unprecedented measles outbreak", denied the parents' request to let unvaccinated children return to the Waldorf School.
It will be enforced the same way any law is enforced, according to Lyon: During the investigation into when and where an infected individual was exposed, those who are identified as unvaccinated and people in public places will be referred to the district attorney's office.
Anyone told by a health care provider to "watch for measles" after possible exposure is advised to stay home and not go out in public, where they could expose others. "This type of response is unacceptable and irresponsible".
The state legislation's Democratic sponsors said too many parents believe unsupported claims that vaccines are unsafe and cause autism or other conditions. "We just want to encourage everyone to do the right thing so we can stop this outbreak", Lyon said. "We don't want to see a repeat of how this outbreak started when we saw people gathered together and then fall ill last fall". So far in 2019, 314 cases of measles have been confirmed in 15 states.
Children are most at risk from measles, according to the CDC.