Three people have died from the flu so far this winter season.
324 people have also been hospitalised, according to figures from the Health Protection Surveillance Centre.
A sample of GPs' surgeries across the country reported an elevated number of flu cases last week and it found that Dublin is the worst affected county so far.
There is localised activity across the country, but the highest number of cases is in the region covering Dublin, Kildare and Wicklow.
Flu sets in far more quickly than a cold and symptoms include a high temperature, body aches, a dry cough and a headache.
The HSE is asking people to stay home from work or school if they are displaying symptoms of flu.
Meanwhile, almost 1 in 3 pupils in a Co. Meath school were out sick on the same day earlier this week.
110 children out of the 364 at O'Growney National School in Athboy were out this week due to seasonal bugs and viruses, including the flu and the winter vomiting bug.
According to the Irish Independent, the school has asked parents not to send a child to school if they're feeling unwell.
