This has resulted in observers warning of outbreaks of measles and mumps in poorly covered areas.

Some parents prefer a single vaccine

Last month, 500 pupils at Denbigh High School, in north Wales, were given the MMR vaccine following an unconfirmed outbreak of mumps.

Seven youngsters were kept away from the school after exhibiting "mumps like" symptoms following five suspected cases.

In February, North Wales Health Authority revealed 82% of children under one year receive the first dose of MMR, which then drops to 66% for the second dose.

The average take-up rate across Wales is 84.5% and 71.0% respectively.

The second dose is important because up to one in 10 children could develop measles or mumps without it.

Health chiefs are anxious to push vaccination levels up to the 'safe' level of 90% for both jabs.

During a board meeting on Thursday, Wrexham Local Health Group is due to discuss initiatives of boosting the take-up rate.

The number of children who are not immune to measles is increasing

North Wales Health Authority

North Wales Health Authority's immunisation coordinator David Morgan applauded the health group's scheme.

"Local initiatives need to be developed where take-up rates are poor," said Mr Morgan.

"We have had no cases of measles in north Wales for the last four years, except for one imported case from the outbreak in Dublin last year, which killed two children.

"However, the number of children who are not immune to measles is increasing and 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.

"The same is true of mumps and rubella."

The authority reported that during the past two years, the North Wales Public Health Department had brought in new plans to boost the level of MMR uptake.

Promotion campaign

Health chiefs distributed an MMR Mythbuster pack for health professionals and parents.

Special training days have also been arranged at GP practices and health clinics to promote the advice packs.

Other health authorities in Wales have reportedly asked for information packs to use in their own awareness campaigns.

Now the Welsh Assembly has set about printing bilingual copies for distribution to all GPs and health visitors throughout Wales.