A 13-year-old boy has become the first person in the UK in 14 years to die from measles.
The MMR vaccine was introduced in the UK in 1988
The victim was from a travelling family living in the north-west of England, the Health Protection Agency said.
A string of outbreaks mainly in England and Wales's travelling communities has led to 100 cases so far in 2006, compared with 76 in the whole of 2005.
The boy, who was suffering from an underlying lung condition, had not had the measles, mumps and rubella vaccine.
The HPA confirmed on Monday it was the first fatal case of measles in the UK since 1992.
A spokeswoman said the teenager had also been taking an immunosuppressive drug for his lung condition.
The Department of Health and the HPA insist that the high number of cases is not due to low take-up as a whole of the MMR vaccine which was linked to an autism scare.
They say the cases have mainly been seen in travelling communities which are traditionally less connected with their local health system and thus less likely to have vaccinations.
However, they say the case underlines the need for all parents to ensure their children are vaccinated against the disease.
Staff at a hospital in north west London are being vaccinated for measles after six employees contracted the disease.
The outbreak at Central Middlesex Hospital happened after two children were brought in with measles.
Health officials say 95% of children should receive MMR so that vaccination programmes are effective, but take-up rates in the UK stand at 82%.
Many parents were put off from vaccinating their children with MMR after research linked the vaccine with autism.
Concern over the jab was sparked by a paper published in The Lancet in 1998 by Dr Andrew Wakefield.
But a more recent study in the same journal concluded there was no evidence of a link between the jab and autism.
Immunisation rates fell as low as 80% in the wake of the scare.
But the Department of Health argues the three-in-one jab is the best way of safe-guarding children because it offers the greatest protection per jab and many parents forget to bring their children for follow-up doses.
The HPA, which monitors disease rates, said this year's 100 measles cases occurred in all regions apart from the North East with victims aged between one and 35.
The first outbreak was seen on a travellers site in Essex in 2005 and the majority of cases since have been associated with the travelling community.
The HPA said two of the cases had received one dose of the MMR and three others had been vaccinated with the single measles vaccine.
Children are given a first dose of the MMR vaccine between 12 to 15 months old and a second, booster dose, at between three and five years old.
A spokesman for Sense, a deaf blind and rubella charity, said MMR take-up rates had dropped over a number of years but were increasing again.
He added that MMR was the best way to protect against the disease.