Teenagers are most at risk from the outbreak

There have now been more than 250 cases in the county this year.

Health experts are now advising young people to go to their doctor for the MMR jab.

Mumps causes flu-like symptoms and swelling of the glands, but occasionally can lead to more serious problems, including meningitis.

Dangerous complications

The outbreak had been confined to the west of the county, but there is evidence that cases are spreading east.

The mumps virus can in some cases lead to uncommon but dangerous complications.

Cornwall Public Heath Director Dr David Miles said: "You can get inflammation of testicles in men, or ovaries in women. On rare occasions this can lead to sterility.

"You can also get side effects such as meningitis."

Many in the age group affected have never received the MMR vaccine or a booster and this has left them vulnerable.

Cornwall GP Dr Philip Dommett said: "Those who are at school or college are being advised to have it done there.

"But for those who are not in education, it would make sense for them to contact their own doctors."