"We expect there to be an outbreak of measles at some point in the future. We don't know when it will be, but it will be very sudden when it does happen

Dyfed Powys Public Health Consultant Dr Mac Walapu

The risk of a measles outbreak increases when take-up levels fall below 85% which is the case in three of Wales's five health authority areas.

They are: Iechyd Morgannwg Health, covering Swansea, Neath Port Talbot and Bridgend; North Wales and Dyfed-Powys.

Although measles is often thought of as a mild illness, it is still considered a potentially serious childhood condition by doctors as more serious cases can cause blindness, brain damage and even death.

Before the MMR vaccine was introduced in 1988 there were 76,000 cases of measles and 16 deaths per year.

Since 1992 there have been no deaths from measles and only 100 cases in 2000.

Oliver Loch and his mum Julie

North Wales has not had a measles case for four years but last year it dealt with one of the youngsters from an outbreak in Dublin which left two children dead.

Health authority immunisation co-coordinator David Morgan said the number of children not immune to measles was increasing.

"We have the same concerns as national bodies that children are increasingly becoming susceptible to measles and we may have cases in the near future," he said.

"The same is true of mumps and rubella."

The health authority is concerned that the low vaccination rate stems from people's fears that the MMR jab is linked to the diagnosis of autism in a small number of children who have had the injection.

Julie Loch

It has launched an "MMR Mythbuster" pack to try and improve vaccine take-up.

In Dyfed-Powys, another at-risk area, MMR rates are some of the lowest in Wales.

Public Health Consultant Dr Mac Walapu said: "We expect there to be an outbreak of measles at some point in the future.

"We don't know when it will be, but it will be very sudden when it does happen."

The average rate for the health authority area is 82.4%, but in Carmarthenshire it has fallen to 78.9% while in Llanelli it has dipped as low as 75.7%.

But the region with the lowest MMR vaccine take-up is covered by Iechyd Morgannwg Health.

The average rate for Swansea, Neath Port Talbot and Bridgend is 80%.

Many parents are hostile to the idea of giving their children the MMR vaccine after research by Dr Andrew Wakefield, who suggested there was a link to autistic-like disorders and bowel problems.

Andrew Wakefield: Expressed concerns

His work has led to the current calls for the single-jab measles vaccine to be reintroduced for those parents concerned about their child having the triple vaccine.

Dr Wakefield was forced to resign from the Royal Free Hospital in London in the autumn of last year - to the outrage of Cardiff mother Julie Loch whose son, Oliver, he had been treating.

Oliver has been diagnosed as autistic and suffers a severe bowel disorder, problems his mother believes were triggered by the MMR vaccine which he had when he was 14 months old.

Mrs Loch said it was time for the government to reassess its opposition to single vaccine treatment.

She said: "It needs to be looked at - parents aren't convinced, they don't really trust what the government says.

Large outbreaks

"I really think that as a matter of responsibility, they should bring the single vaccines in."

A spokeswoman for the assembly said doctors remained concerned that the low level of MMR usage left Welsh youngsters exposed to the wild form of measles as well as mumps and rubella.

"Our target is 95%. Where rates are lower that this there is a risk of insufficient levels of protection in the population and the likelihood of large outbreaks of all three diseases is greatly increased," she said.

Speaking at the assembly's health committee meeting on Wednesday, Wales's Chief Medical Officer, Dr Ruth Hall, told the assembly the single vaccine would not give the same coverage as MMR.

She said it would also divert the scarce time of medical staff.