Sheffield University has issued an official warning of a potential outbreak of mumps after writing to all its students, recommending that they be vaccinated against the "potentially serious" disease before starting the new term.

The move follows an outbreak of the virus in the spring which started at the university, infecting 150 students and spreading to 80 others at neighbouring Sheffield Hallam University and in the community. The outbreak was the biggest since the measles, mumps and rubella (MMR) vaccination was introduced in 1988.

Before last Easter break, the university initiated a mass vaccination of 7,000 students.

Dr Rosy McNaught, consultant in communicable disease control at the Health Protection Agency (HPA) said: "The people we are worried about are between the ages or 16-25.

"The older you get, the more likely you are to have had natural infection," she added. "24 to 25-year-olds have very few cases. People below 16 have usually had at least one dose of MMR. Those who are between 16 and 25, as kids, were too old for the MMR vaccine, so they would not have had mumps vaccine at all."

According to the HPA, 70% of 18-year-olds are believed to be vulnerable to the virus.

Dr McNaught added that there was no official nationwide warning yet: "There will be other universities which have had outbreaks which may consider the same action. But we have had 230 cases, 21 of which ended up in hospital. It is not very nice when you come to university and end up in hospital because of mumps... which is entirely preventable."

Sheffield is recommending that all its students are immunised with the controversial MMR jab at last three weeks prior to arriving at university.

In most people the mumps virus causes very little upset and may even go completely unnoticed. But in others it can have some quite severe complications including meningitis, encephalitis, deafness and sterility. Symptoms include headache and fever, followed by swelling of the glands in front of the ears on one or both sides.

The university is also asking medical, dental nursing and speech science students to have hepatitis B immunisation and screening for hepatitis B antigen before they start their course.

Students are being advised to contact NHS Direct on 0845 46 47, for advise on where to get immunised.