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DALLAS (KRLD 1080) – One Dallas County school is dealing with a major mumps outbreak.

Twenty-three students and staff at Cedar Hill High School were diagnosed with mumps in the past three weeks, and an additional 9 cases are under investigation.

Dallas County health director Zach Thompson says all the students diagnosed have had their two doses of mumps-containing vaccine.

“We may be dealing with the fact that the vaccine has waned and we will be dealing with a third dose recommendation in the future.”

As to what’s causing the outbreak, Thompson says there may be other factors.

“Those who are opting of getting the vaccine for their children or people traveling overseas.”

There has been an increase in mumps in north Texas over the past few months with more than 70 confirmed cases.

Mumps, which is spread through the saliva or mucus of an infected person, is known for its symptoms of puffy cheeks and a swollen jaw and may be accompanied by a fever, aches and fatigue. Some people may remain without symptoms.

There is no treatment for mumps, but most people recover completely in a few weeks.