New York ( CNN ) -- More than 1,000 people in New Jersey and New York , many of them adolescent Orthodox Jews , have been sickened with mumps since August , health authorities said Monday . Orange County , New York , has confirmed 494 cases since early November , county spokesman Richard Mayfield told CNN . Almost all of those infected with the virus are of the Orthodox or Hasidic Jewish population , and their average age is 14 , he said . Neighboring Rockland County has confirmed 317 cases since August , with all of the sick from the Orthodox Jewish community , said Kathleen Henry , county Deputy Commissioner of Health . Their average is 14 to 18 , she said . Just south of the two counties , in New York City , Brooklyn had 79 confirmed cases of mumps as of October 30 , the Centers for Disease Control and Prevention reported in November . Any confirmation of other infections in the city are expected to be announced Tuesday . The mumps outbreak began at a summer camp for Orthodox Jewish boys in Sullivan County , New York , according to the CDC . Health officials have linked the outbreak to an 11-year-old boy at the camp . He had recently returned from the United Kingdom , where a mumps outbreak had spread to 4,000 people . The mumps outbreak also spread to Ocean County , New Jersey , where 159 confirmed cases have been diagnosed since September , county spokeswoman Leslie Terjesen told CNN . An additional 70 others are suspected of having mumps , she said . Only seven of the infected are not Orthodox Jewish , but they all had exposure to the community , Terjesen said . The average age of the sick is 21 , she said . Lakewood , New Jersey , Rabbi Yehunda Pirutinsky was surprised when his 14-year-old son was diagnosed with mumps a week ago . Lakewood is in Ocean County . `` He was completely vaccinated , '' Pirutinsky said . `` So it was a surprise to us he came down with mumps . '' Anyone fully vaccinated from mumps receives two doses of the vaccine , according to the CDC . Of the New Jersey cases , 77 percent were vaccinated , Terjesen said . But the vaccine is not 100 percent effective , according to the CDC . At two doses , the vaccine is 76 to 95 percent effective , the CDC says on its Web site . In November , the CDC called the spike in mumps cases , `` the largest U.S. mumps outbreak since 2006 , when the United States experienced a resurgence of mumps with 6,584 reported cases . '' Then , only 179 people were sickened in New York and New Jersey . Mumps is a contagious disease caused by a virus , according to the CDC . Initial symptoms appear 12 to 25 days after infection and include fever , headache , muscle aches and loss of appetite . Mumps can cause the jaw and cheeks to swell , with further complications including the inflammation of the brain , testicles or ovaries , and deafness , according to the CDC . Pirutinsky 's son has fully recovered from his bout with mumps , which Pirutinsky assumes he contracted while at his Jewish high school . A doctor advised the teenager to not attend school for a week and limit time with his siblings , Pirutinsky said . The outbreak has disproportionately affected Orthodox Jewish communities , but Pirutinsky said he was n't overly worried . `` I would n't say the community is alarmed , but it 's something we 're aware of , '' he said . CNN 's Edmund DeMarche , Miriam Falco and Nicole Bliman contributed to this report .
Almost all the cases of mumps involve adolescent Jews Orthodox . Outbreak traced to boy who went to U.S. during mumps outbreak . Severe cases of mumps can lead to brain inflammation and deafness . It 's the largest outbreak in the United Kingdom since August .