Outbreaks of mumps have become widespread around the country, the Health Service Executive has said.
There were 132 cases of mumps reported to the Health Protection Surveillance Centre last week.
Mumps is a highly contagious viral infection, and the most common symptom of mumps is a swelling of the parotid glands.
The glands are located on both sides of the face and the swelling gives a person a distinctive 'hamster face' appearance.
Speaking on RTÉ's Morning Ireland Dr Kevin Kelleher, the HSE's Assistant National Director of Public Health, said it is happening because a large portion of 15-30 year old people have not got full protection against mumps.
He said not all of them are getting the MMR vaccine or are only getting one dose, when people need at least two doses to be fully protected.
The HSE is warning schools, colleges and universities about the outbreak.
A Specialist Registrar with the HSE's Health Protection Surveillance Centre said it was "very concerning to see a sustained spread of mumps, due to the serious complications that can arise" from the viral infection.
On RTÉ's Six One, Dr Mark O'Loughlin said people should check their own health records to ensure they are fully vaccinated.
He said those who are unsure if they are fully protected should avail of a free-of-charge booster dose, which he said will not cause any harm to anyone.
Dr O'Loughlin said people can get this booster dose from GPs, or at their student health centre.