A senior doctor has repeated her call for parents in Cardiff to have their children vaccinated with the triple dose MMR - measles, mumps and rubella - jab.
The uptake of the MMR vaccine has been in decline across Wales
A total of 19 children are now believed to have contracted measles in an outbreak which is the first in Cardiff in a decade.
Eight cases of the potentially fatal disease have been confirmed, while laboratory tests are expected to confirm the remainder in the next few days.
Dr Marion Lyons, Consultant in Communicable Disease Control at Bro Taf Health Authority, has suggested parents need to overcome their apprehension about the MMR jab.
Vaccination rates in Bro Taf Health Authority, like those across Wales, have been falling since the controversial claim in 1998 that the combined MMR vaccine was linked to the development of autism in some children.
However, no research has yet to provide conclusive proof that such a link exists and a number of studies have suggested there is no link between the jab and autism.
Take-up of MMR jab has fallen after fears about its safety
Dr Lyons said she wanted parents who had not given their children the vaccine to think again about their position.
She said: "Measles has got a foothold again - we had almost eradicated it UK-wide by 1995, but it's back and I'm asking them to reconsider.
"Are they going to go for the unfounded allegations against a safe and effective vaccine or are they going to consider their child is possibly the one-in-500 who might die if measles spreads into the community?
"And when we have low uptake rates, the virus will find its way around from one vulnerable child to another."
The latest available figures show the MMR take-up rate in the health authority area has fallen to 85.7% of children, down from 87.4% in January last year.
The average take-up rate for MMR in Wales is 83.8%.
Health experts said the cases, all in the east of the city, appeared to be linked.
The World Health Organisation recommends 95% of children in a population need to be vaccinated to prevent the disease from spreading.
Measles remains a killer in the developing world, taking the lives of around one million children worldwide.
The number of cases in England and Wales has tripled in recent years and is at its highest since the MMR vaccine was introduced in 1988.
Experts say it once again raises concerns that the fall-off in numbers of children having the combined vaccine will lead to increasing outbreaks of the disease.
The symptoms of measles are feeling unwell, fever, sore eyes, cough and red blotchy rash, which spreads from the face all over the body.
If a child develops these symptoms, a doctor should be contacted.