Teenagers and young adults are being struck down by mumps as last year's outbreak of the highly infectious disease continues into 2020.
There were 193 cases of mumps reported in the first two weeks of the year, and third level students are among the worst affected.
The east of the country, including Dublin, has seen the biggest number of mumps cases.
The HSE has again urged people who have potential symptoms, such as swollen cheeks or jaw, to stay at home and not go to school or work.
The best protection against mumps is to be fully vaccinated with two doses of the MMR (Measles-Mumps-Rubella) vaccine.
Although most people recover from mumps without any serious side effects, the virus can lead to complications, including swelling of the pancreas or liver, and even meningitis.
A surge in cases is linked to a fall in the uptake of the MMR vaccine two decades ago.
The current generation of students were born at the height of a mass health scare triggered in 1998 by disgraced doctor Andrew Wakefield, who wrongly made a link between the vaccine and autism.
Other symptoms of mumps can include fever, headache, tiredness, and swollen and tender salivary glands - usually the parotid gland, just below the front of the ear.
Between January to the end of November last year there were 2,370 cases of mumps, compared to a total of 573 for 2018.
Most cases are in the 15-24 age group. Among those in this group, school, university, college or social settings were reported as the most likely place to be infected by mumps.
All children should get the MMR vaccine at the age of 12 months. If any child over 12 months has missed this vaccine, they should get it now from their GP.
Children should get a second dose of MMR vaccine when they are four to five years old.
If any child in senior infants or older has missed this vaccine they should get it now from their GP. Teenagers and adults under 40 years who have not received two doses of MMR vaccine should also contact their GP to get the vaccine.