Nearly 4,000 cases of mumps have been reported in Ireland over the past 18 months, mainly among young people, according to a new study.
The study by HSE researchers for the Mumps Outbreak Control Team found the age groups most affected in the current outbreak - those between 15 and 24 - were born around the time of low MMR vaccination uptakes in the early 2000s.
The current generation of students were born at the height of a mass health scare triggered in 1998 linking the vaccine and autism, which has since been debunked.
"The low vaccine uptake reported in 2001/02 was attributed to a lack of confidence in MMR at that time, which led to some parents refusing or delaying vaccination of their children," said the study.
The report published in Eurosurveillance - Europe's journal on infectious disease surveillance, epidemiology, prevention and control - revealed there were 3,736 mumps cases notified here between August 18 2018 and January 24 this year.
The researchers said the outbreak was continuing strongly into 2020, with the largest number of weekly mumps notifications, numbering 302 cases, in the last week of January.
This is compared with only around a dozen cases of mumps reported in January 2019.
Ireland is among a number of countries, including the United Kingdom, the Netherlands, Czech Republic, Israel and the United States, who have reported large mumps outbreaks involving mainly adolescents and young adults in recent years.
"The high potential for transmission in the crowded social environments of students, eg, large indoor gatherings and shared housing, only partly explains the ongoing outbreak," said the authors.
But they added: "Other additional factors need to be considered, such as historical low uptake of MMR vaccine, insufficient effectiveness of the mumps component of the MMR vaccine and the possibility of waning immunity in those appropriately immunised."
The study found vaccination status was reported for 32pc of cases, with three out of four reporting they had received two doses of MMR, but these figures were based on recall in some cases.
Nearly one in 10 of those with mumps had some sort of hospital treatment due to the illness,
Information on any complications was reported for 651 cases, with 13pc experiencing some complications including orchitis, meningitis, pancreatitis and encephalitis.
The HSE experts said a free MMR vaccination programme has been targeted at third-level institutions as the outbreak predominantly has affected colleges and universities.
In 2019, all students - including those in secondary school and education staff under 25 - who had not received two doses of MMR were recommended to get vaccinated.
But data from the HSE drugs payment programme shows the number of doses of MMR administered under the code specifically created for outbreaks has been low.
The authors said they are trying to raise awareness among those aged 11 to 30 across Ireland to ensure they have received two doses of MMR.