However, according to latest figures, cases of measles are increasing – and, with millions of children unvaccinated against the disease, experts have warned that if it could spread with devastating effects.

While the majority of cases involve unpleasant but not serious symptoms, complications, which occur in 10 to 15 per cent of cases, can include severe breathing difficulties, ear infections, pneumonia and conjunctivitis.

About one-in-200 children with measles have convulsions, but the most serious problems involve the nervous system. Inflammation of the brain, or acute encephalitis, affects fewer than one in 1,000 measles cases – but 25 per cent of those are left with brain damage. The slowly progressive brain infection SSPE (subacute sclerosing pan-encephalomyelitis) is the most severe complication of measles, and usually occurs years after the initial illness.

"It's more common if children get measles very young, at under a year," says Dr David Elliman, a consultant in community paediatrics at Great Ormond Street Hospital for Children. "About seven or eight years after having measles, they lose intellectual function, become uncoordinated, fall over, develop seizures, and then die. The virus lingers in the brain – but it is quite unusual."

Fortunately, SSPE occurs in fewer than one in 100,000 cases of measles and while anyone can suffer complications, the most vulnerable are the malnourished or those already suffering from abnormalities of the immune system.

Certainly, a 17-year-old boy who died earlier this year after contracting measles and then developing pneumonia, had been born with a poor immune system, leaving him susceptible to infections and unlikely to have been able to be immunised.

And a 13-year-old who died in 2006 after getting measles also had a weakened immune system, and died of an infection of the central nervous system.

"You may not be able to immunise children with immune system problems, and the only way they're protected is if you can get rid of the disease by immunising everybody else – the so-called herd immunity,"
says Dr Elliman. "Immunisation is primarily to protect your
own child, but it does have the knock-on effect that by getting lesser amounts of the disease around, people who can't be immunised will also
be protected."

On paper it all sounds so simple. Not only are children protected against measles by the MMR vaccine, but also mumps and rubella. While these two generally have less serious complications than measles, doctors want to protect people from rubella because of the severe damage it can do to unborn babies, and mumps because, until the vaccine
was brought in, it was the most common cause of viral meningitis.

However, uptake of the MMR jab fell to an all-time low after
a now discredited study suggested that the triple vaccine was linked to autism and bowel disease. As a result, measles cases have risen sharply in recent years – there were 1,726 cases in 2006 and 2007 in England and Wales, which is more than in the 10 previous years put together, when there were a total of 1,621 cases.

"Measles is undoubtedly a serious disease – it was killing quite a lot of people before we had a vaccine," says Dr Elliman.

"And the best way of stopping unborn babies being damaged by rubella is by immunising everybody and trying to get rid of the disease.

"Mumps, although it doesn't usually cause any permanent problems, can be very unpleasant if you get a mumps meningitis. People need protection."

The Health Protection Agency (HPA) has warned that the number of unvaccinated children is now large enough to sustain the "continuous spread" of the measles virus, and doctors are desperate to push vaccination rates back to the level before the controversy over the MMR vaccination in the late 1990s.

The Department of Health is making extra doses of the vaccine available, and has asked NHS trusts to offer it to all those aged up to 18 who aren't already fully protected against measles, mumps and rubella.

The latest HPA research suggests that there is now a
real risk of a large measles outbreak of up to 100,000 cases, although Professor Elizabeth Miller, the HPA's head of Immunisation, stresses that vaccination uptake has improved.

"Public confidence in the MMR vaccine is now high, with more than eight out of 10 children receiving one dose of MMR by their second birthday," she says. "However, low vaccine uptake over the past decade means there's now a large group of children who either haven't been vaccinated or who've received just one dose.

"These children are susceptible to not only measles but to mumps and rubella as well.

"It's not possible to tell who'll be seriously affected by measles," she continues.

"This is why it's incredibly important to continue to remind parents about the benefits of having their child vaccinated with two doses of MMR for optimum protection.

"It's never too late to get vaccinated."