Most people in the U.S. have been vaccinated against this, but outbreaks still pop up here and there. For example, a 2009 outbreak in the Northeast affected more than 3,000 people. These tend to happen where a bunch of people live close together, like a college dorm. It can cause fever, headache, and tiredness. But the main symptom is pain and swelling in your jaw and cheek in front of your ears. In rare cases, it can also lead to swelling in the brain, breasts, ovaries, and testicles.