Starting December 7, some children in Brooklyn will not be allowed to attend school if they haven't had their measles, mumps, and rubella vaccine.

The City Health Department is cracking down amid a measles outbreak in Williamsburg and Borough Park. Sources said they believe the outbreak is completely contained within the orthodox Jewish communities in the neighborhoods.

Officials are requiring every student attending schools in those neighborhoods to get vaccinated.

There have been 39 confirmed cases so far since the outbreak began in October, and more up in Rockland County.

The Department of Health says it began after families traveled to Israel, where there's currently a large outbreak underway.

The Department of Health says children attending day care or pre-k must have at least one dose of the MMR vaccine. Children in kindergarten through 12th Grade must have two doses of the vaccine.

Religious exemptions will not be honored. Those children will have to stay out of class until the outbreak is considered over.