Measles is coming back with a vengeance, the Health Protection Agency warned yesterday.

More than 480 cases of the childhood illness have been reported so far this year and the number has trebled since June. This compares with 756 cases in the whole of 2006, which was the highest total since the current method of monitoring was introduced more than a decade ago.

Worst hit is London and the South-east, where almost half of the cases have occurred. The east of England has also seen outbreaks of the illness accounting for more than a quarter of the total.

The HPA said that just 136 cases had been confirmed by 10 June, but that the total had risen to 480 by 24 August, a higher rate than usual for the time of year. The agency urged parents to have their children vaccinated before they go back to school in September.

Dr Mary Ramsay, a consultant epidemiologist at the HPA, said: "We have had quite a few cases in children of school age and we are worried those cases are going to take themselves into school when term starts soon. Although the numbers are still small, we are always worried about it because very rarely it can kill.Measles is a highly infectious and dangerous illness and, as there is increased close contact in schools, it can spread easily.

"Now is the time parents will be buying their children a new school uniform to prepare for the school year ahead, but being prepared to avoid infection is even more important.

"Parents should think about adding the MMR vaccine to their back-to-school 'to do' list."

Confidence in the MMR jab was severely hit by research published in The Lancet in 1998 suggesting a possible link with autism. National vaccination rates fell from a high of more than 90 per cent to 79 per cent in 2004 and to below 50 per cent in some areas of London and elsewhere.

Subsequent studies failed to confirm the link and the chief author of the Lancet paper, Andrew Wakefield, is currently appearing with two colleagues before the General Medical Council charged with serious professional misconduct. The case is expected to conclude in November. All three doctors deny the charges.

In Hackney, east London, there have been 120 cases of measles in the past three months – most of them in children under five who have not been immunised.

Michael Fitzpatrick, a local GP, said he was angry that the campaign against MMR had ended with outbreaks such as this. "This was inevitable and the only surprise is that it hasn't happened earlier and hasn't happened on a bigger scale."

Vaccination rates have improved since 2004 and stand at about 84 per cent. But a rate of 90-95 per cent is needed to ensure "herd immunity" – the protection of all children including the unvaccinated. In April last year, a 13-year- old boy from Manchester became the first person to die from measles in the UK for 14 years.

The HPA said it was difficult to know why there had been such a jump in measles in recent weeks. Cases were higher in communities where vaccine uptake was lower, including travelling families. But cases were also occurring in unvaccinated school-age children across all social groups.

There have also been small outbreaks in primary schools and cases in people returning from other countries, a spokeswoman said.

Dr Ramsay urged parents to make sure their children received two doses of the MMR vaccine – one at 12-15 months and a booster at four before starting school. She said: "Public confidence in the MMR vaccine remains high as the uptake for those receiving their first dose has stayed stable. But children should complete their full course of MMR vaccine."

A Third World killer

Measles is a highly infectious virus that causes a fever and conjunctivitis, followed by a rash three to five days later. The rash lasts about a week and the virus may also cause pneumonia and diarrhoea. It is one of the most infectious diseases known and spread rapidly in epidemics before the introduction of vaccination in the late 1980s. Before this there were about 20 deaths a year on average in the UK. In the developing world millions of children die each year from measles. There is no treatment other than child versions of paracetamol or similar drugs to reduce fever and muscle aches.