The outbreak has mainly been isolated in a couple of communities within Rockland County, which is just north of New York City, but the whole community is at risk, he said, noting that there have been complications among patients, including a premature labor and a handful of hospitalizations.
According to the Associated Press, Day said at a new conference Tuesday that the move - which will be in place for 30 days, during which violators "could be charged with a misdemeanor punishable by up to six months in jail" - was "an attention grab" meant to drive home the importance of vaccines.
Despite the ban, Day says the government will not engage in a crackdown by chasing unvaccinated people and hounding them into being "a part of the solution".
Measles is a highly contagious respiratory disease caused by a virus that is spread by direct contact with nasal or throat secretions of infected people.
"This is a public health crisis and it is time to sound the alarm and take the appropriate action", Day said.
From Jan.1 to March 21, there have 317 cases of measles reported, with outbreaks having been reported in California, Illinois, New York, Texas and Washington.
Day also said he believes the ban is an unprecedented step in the US, reported the AP.
More than 300,000 people live in Rockland County, which has reported 153 cases of measles since last October, according to The New York Times.
About 30 people got measles vaccinations at a free county clinic Wednesday. "They have been hung up on or told not to call again", Day continued in Tuesday's news release. "This type of response is unacceptable and frankly irresponsible". However, he said, parents and guardians who are found to be in violation will be held accountable and their cases will be referred to the district attorney's office.
"They have been supportive of what we've been trying to do", Day said. In less than 24 hours, the number of confirmed cases went up to 155. That order-and the directive issued today-are meant to thwart the long-standing outbreak, which has sickened 153 people, mostly children.
Places around the world have started taking preventative measures to ensure that unvaccinated people don't make the rest of us sick.
In September of a year ago, an global traveler arrived in Rockland County with a suspected case of the measles. Early on in the outbreak, county residents were more receptive to getting vaccinated.
This year, 314 cases have been reported nationwide, according to the CDC.