Universities and military bases are stepping up efforts to ensure students and new recruits are innoculated against mumps as the disease makes a painful comeback.
There were 1,529 confirmed cases in England and Wales last year, three times the figure in 2002, and double the number in 2001, which prompted a previous government appeal for all unvaccinated teenagers to be immunised.
Mumps is at its highest level since at least 1995, when a new surveillance system was introduced confirming illness by saliva tests.
Nearly all those falling ill to the condition, with its distinctive swelling to the sides of the face, are now in their teens or early 20s, since they missed the introduction of the triple measles, mumps and rubella jab in 1988, or only had one of the two doses.
The disease is no longer a big threat among the under-10s because of immunisation programmes, but repeated advice that all adolescents and young adults should have it in two doses three months apart has not been universally followed.
Around 1,200 children and young people a year used to be admitted to hospital with mumps. Before MMR's arrival there had never been a vaccine against the disease.
The present epidemic is not on the same scale, and mumps is rarely fatal. But officials are concerned because the disease, easily spread between unimmunised people, is now hitting mainly young men at an age when the symptoms can be a lot more painful. These include inflammation of the testes, although sterility is a rare consequence.
Other complications include meningitis and, in very rare cases, deafness in one ear. Mumps can also cause women problems with their ovaries and spontaneous abortion early in pregnancy.
Vaccination should give lifelong immunity but mumps could pose problems for the rest of the decade unless more is done to tackle the threat.
Government advice after 1996 was that all students who had not been immunised against measles and rubella should be offered the MMR jab. This was updated three years ago to say the triple vaccine should be given to all teenagers who had never had it or only one of the two doses. It is given to babies between 12 and 15 months and again between the ages of three and five.
The Health Protection Agency said yesterday: "It is unclear how many teenagers are not properly protected but current outbreaks indicate that susceptibility remains high. Some universities and military establishments have offered MMR to first-year entrants and others are considering taking similar action."
Provisional figures also suggest big increases in measles cases, up to 442 last year from 310 in 2002 and just 70 in 2001. Much of the rise is blamed on infection within travelling communities, where take-up of the MMR vaccine has been poor.
MMR vaccination rates in children improved for the second quarter running at the end of 2003, with more than 81% having had the first jab before they were two. Officials are watching closely to see if this improvement continues following last month's furore over the credibility of the research that suggested a link between MMR and autism.
