The MMR vaccine protects against mumps, measles, and rubella
Eight new measles cases have been diagnosed amid warnings that the disease is on the increase due to a reduction in the take-up of a vaccine.
The cases in Wrexham and Flintshire take the total number of diagnosed cases in the region to 21.
It follows an outbreak of 13 cases in Carmarthenshire and two in Cardiff.
Dr Chris Whiteside from the National Public Health Service for Wales (NPHSW) said diagnosis of measles was higher than last year.
She said 79% of five-year-olds in Wales had been given the two recommended MMR jabs - against a UK government target of 95%.
She blamed a "legacy of doubt" following a report that MMR could be linked to autism, which has now been disproved.
Dr Whiteside, consultant in communicable disease control, said: "Measles is a highly contagious infectious disease and children who have not been immunised are at risk.
"Most people who catch measles make a full recovery but there is a rare possibility of severe complications including serious eye disorders, deafness, mental difficulties and even death."
She added: "We would urge people to use the MMR vaccine.
"There's a significant increase of measles in Wales. For instance we haven't had a case in north Wales since 2006, but already we have had 21 suspected cases this year."
Earlier this month, it was also revealed 13 students and staff at Newcastle Emlyn Comprehensive School in Carmarthenshire were diagnosed with the illness.
Two family members of one of the pupils who live in Cardiff, were also thought to have measles.
With 36 suspected or diagnosed cases this year, Dr Whiteside said it was likely the number of confirmed cases for Wales would rise above the total for 2007 of 14.
The outbreak in north Wales has not been linked with that in the south.
Letters have been sent to GPs in north Wales to alert them to a possible increase in demand for MMR.
The NPHSW said some of the cases diagnosed by GPs could go on to be proved negative.
Of the 21 clinical cases reported in north Wales, eight samples are awaiting results and nine have been confirmed as measles.
Two cases proved negative and two are being re-tested.