Signs about measles and the measles vaccine are displayed at the Rockland County Health Department in Pomona, N.Y., Wednesday, March 27, 2019.

New York City is threatening to close some Jewish schools in Brooklyn that allow unvaccinated students as a measles outbreak in the area worsens.

The city in December ordered Orthodox Jewish schools and child-care centers in some areas of Brooklyn to ban unvaccinated children from attending. In January, one yeshiva ignored the mandate and welcomed unvaccinated children. That one incident is now linked to more than 40 cases of measles, the health department said Tuesday.

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Yeshivas and child care centers in the Williamsburg neighborhood in Brooklyn that refuse to comply with the city's order may be fined or even closed, the city's health department said Monday. This comes just weeks after nearby Rockland County banned unvaccinated children from public places, an order a judge has since struck down.

"This outbreak is being fueled by a small group of anti-vaxxers in these neighborhoods. They have been spreading dangerous misinformation based on fake science," New York City Health Commissioner Dr. Oxiris Barbot said in a statement.

Since October, there have been 285 cases of measles in New York's Orthodox Jewish community, the health department said. Health officials traced the first case of this outbreak back to unvaccinated people who traveled to Israel, where there is a large outbreak. Other New Yorkers have since caught the disease traveling in Israel, Ukraine and the U.K., the health department said.

Some ultra-Orthodox Jews have refused to vaccinate their children, leaving the tight-knit communities vulnerable to the highly contagious disease. New York drove the recent spike in measles cases around the country, pressuring health officials to find a way to contain outbreaks ahead of Passover, which starts April 19.

"We've seen a large increase in the number of people vaccinated in these neighborhoods, but as Passover approaches, we need to do all we can to ensure more people get the vaccine," Barbot said.

So far this year, 465 cases have been confirmed, the second-highest amount since the disease was declared eradicated from the U.S. in 2000, according to the Centers for Disease Control and Prevention.