Image by Avi Katz

New York Mayor Bill de Blasio on Friday urged city residents - particularly Orthodox Jews - to get their children vaccinated as one of the largest measles outbreaks in city history continues to grow, almost solely in Jewish areas of Brooklyn.

“As a dad, I urge all parents — particularly in our Orthodox Jewish community — to vaccinate our children,” he tweeted. “Measles is highly contagious and can be very serious and fatal. The vaccine is safe and effective. Please protect your family and your neighbors.”

The city’s Department of Health and Mental Hygiene stated Thursday that they had confirmed 121 cases of measles in Orthodox Brooklyn since October - a vast increase from the 55 cases reported in January.

The initial cases of the outbreak came from infected people who had traveled from Israel, the United Kingdom or Ukraine. Most cases in the city are confined to the heavily-Orthodox neighborhoods of Boro Park and Williamsburg. The health department said that 21 of the 31 most recently reported cases were connected to a single yeshiva in Williamsburg.

Major Orthodox rabbis and political leaders have urged community members to vaccinate, but many individuals, including some rabbis, still adhere to debunked theories that vaccines cause autism or are otherwise unhealthy.

Related outbreaks have also spread in Orthodox enclaves in upstate New York. The Forward reported in January that 116 cases of measles have been observed in two upstate counties since September.

Contact Aiden Pink at pink@forward.com or on Twitter, @aidenpink