Parents of unvaccinated children are well educated, well-off and have easy access to transport, according to a new study.
It found that parents who opt to delay or refuse vaccines are more likely to depend on the internet and the media for information than those who have their children immunised. Lack of time in families where both partners work outside the home is also a factor, according to researchers.
Louise Cullen, a surveillance scientist in the HSE Northwest area, led the research team whose findings pointed out that there were 1,000 cases of mumps in Ireland last year - compared with just 400 in 2004.
"There is no doubt that reluctance to take up the vaccine was a big factor in that," said Ms Cullen. She said teenagers and college students had been particularly badly hit in the 2005 outbreak "but they had to get it from somewhere".
She said it was reasonable to speculate that negative media reports about the links between the measles, mumps and rubella (MMR) vaccine and autism, in a now discredited but much publicised study, had influenced parents.
International research to date has suggested that insufficient access to transport, high levels of deprivation, low educational attainment as well as adverse media reports and lack of knowledge cause parents to opt out of immunisation programmes. However, this survey indicated different reasons for parents choosing not to vaccinate their children.
The study of about 500 families in counties Sligo, Leitrim, Donegal and west Cavan showed that unvaccinated children tended to come from two-car families where both parents worked and had a high income and educational standard. They were also more likely to have private medical insurance. A comparison of parents who did and did not have their children vaccinated showed that the level of knowledge about vaccines was the same.
The findings were presented at the seventh annual multidisciplinary research conference at Sligo General Hospital at the weekend.
Delegates suggested that given the influence of the internet, it might be more effective to issue vaccine reminders to parents via e-mail and text messages than the standard letter.
While parents were not asked to specify what media reports triggered their fears, researchers believe the controversial Wakefield report suggesting a link between the MMR vaccine and autism was still having an effect.
"We have found when monitoring the immunisation programme that parents bring their children for the MMR when they are two or three when they believe the risk of autism may have passed," said Ms Cullen.
She said it was important to stress that many parents were delaying rather than refusing the vaccines.
The findings also show that with both parents working, time was an important factor in whether children were taken to the GP's surgery for their shots.
"Our figures show that while the uptake of the five-in-one is excellent for babies at two months old, it is slightly down in the four-month category but it falls off considerably at the six- month stage," said Ms Cullen.
She said it was possible that this reflected that maternity leave was over by the time the baby got to six months.
Ms Cullen agreed that an out-of-hours service might increase the numbers of children getting the vaccines: "It is possible that having an out-of-hours vaccination service, possibly on a Saturday morning, might boost the figures."
She stressed that the immunisation uptake in the northwest region had improved significantly to 91 per cent but was still below the WHO recommendation. "We need to reach a level of 95 per cent to protect the population of children with cancer who cannot have the vaccines."
