'Widely discredited' stories on social media are influencing the recent slide in vaccination rates across the country, according to a senior public health official.
The latest figures show vaccination rates have dropped to as low as 81% in some parts of the country.
It comes amid a surge in measles cases across Europe - with the World Health Organisation saying there were more cases reported in the first half of this year than the whole of 2018.
Albania, Czech Republic, Greece and the United Kingdom have all lost their measles elimination status.
The HSE's Assistant National Director for Public Health, Dr Kevin Kelleher, said "widely discredited myths" about vaccines are still being repeated.
''Some intimation is that people are being influenced by some of the less scrupulous messages that are appearing on social media about vaccines, using stories that have been repeatedly discredited, but they still pop up."
He pointed to the work Andrew Wakefield, a former English doctor whose widely discredited research has led to him being struck off the UK medical register.
Dr Kelleher noted: "The myths he put out, they are repeated a lot - but they are totally discredited, and there are no basis to them whatsoever."
He also explained that while inner city areas have had problems with vaccine rates over the years, the rates also aren't as high in more prosperous areas such as Dublin and Wicklow.
He suggested: "People are just listening to some of those messages... that's what's making their decision, as opposed to the information we provide