Over 1,600 cases have been recorded this year.
Parents are being warned about the risk of mumps as kids go back to school this week.
Over 1,600 cases have been recorded so far this year - that's three times the total in the whole of 2018.
The HSE says the way things are going, up to 7,000 children a year won't be vaccinated against measles and mumps. Take-up of the MMR vaccine has fallen in recent years and has reached as low as 80% in some parts of the country.
It's led to outbreaks of mumps in places like universities and schools, some of which will be welcoming students back this week.
Fake news on social media has been partly blamed for the fall off in vaccination rates and the HSE is reportedly working with Twitter to try and combat misinformation online.
