The state health department reported 45 cases of mumps Friday in Orthodox Jewish communities in Spring Valley and Monsey.
According to Rockland County Health Commissioner Joan Facelle, in about a third of the cases, the individuals had been fully immunized before contracting the disease. Many of the cases involve school-age children.
Health officials say they are working closely with the communities to try to stop the outbreak, which they believe started at a summer camp in Sullivan County.
Mumps symptoms include fever, headache and swelling of the salivary gland. The disease can be spread through direct contact with saliva when an infected person coughs or sneezes.