But does such a stark warning really frighten the parents of the millions of British children who are not vaccinated against the disease?

After all, measles is just a mild, common childhood ailment, isn't it?
Certainly, the highly contagious illness usually causes fairly mild symptoms including a runny nose, cough, fever and a blotchy rash which can spread all over the face, neck and body. There can also be diarrhoea, vomiting and abdominal pain.

But while the majority of cases involve unpleasant but not serious symptoms, complications are common.

Dr David Elliman, a consultant in community paediatrics at Great Ormond Street Hospital for Children, says complications occur in around 10 per cent to 15 per cent of cases.

They can include a severe cough and breathing difficulties (croup), ear infections (otitis media), viral and bacterial lung infections (pneumonia), and eye infections (conjunctivitis).

Around 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 less than one in 1,000 measles cases – but 25 per cent of those are left with brain damage.

The slowly progressive brain infection SSPE 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," Elliman says.

"About seven or eight years after having measles, they lose intellectual function, become unco-ordinated, fall over, develop seizures, and then die.

"The virus lingers in the brain – but it is quite unusual."

Fortunately, SSPE occurs in less than one in 100,000 cases of measles.
But Elliman warns: "Anyone can suffer complications, even the well-nourished".

"You're more likely to get complications if you're malnourished or if you have something else wrong with you, like 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 immunised.

And a 13-year-old who died in 2006 after getting measles also had a weak 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," Elliman says.

"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."

However, uptake of the MMR jab fell to an all-time low after a now-discredited study suggested 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.

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

The Health Protection Agency 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 they were at 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 children aged up to 18 who aren't already fully protected.

The latest research suggests that there is now a real risk of a large measles outbreak of up to 100,000 cases, al-though Professor Eliza-beth Miller, the agency'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."

"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.

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