A mumps outbreak among Orthodox Jews in New York and New Jersey has now surpassed 1,500 cases and shows no sign of ending soon.

The outbreak began last summer at a boys camp in the Catskills. Nearly all the cases are in the insular Orthodox Jewish community. Health officials said most had a mumps vaccination, but the shots are not completely effective.

The Centers for Disease Control and Prevention on Thursday said the count has now reached 1,521. Nineteen people have been hospitalized but no deaths have been reported.