Fifteen people, all adults, have died of the flu so far this season.
The HSE says we're still a week or two away from the peak of the flu season.
It is urging vulnerable patients and those over 65 to get the flu vaccine.
Dr. Joan O'Donnell, from the Health Protection Surveillance Centre, said: "We've had a report of 262 hospitalisations with confirmed flu bringing the season total to 535.
"There are 27 cases of flu in critical care units, there have been 15 deaths from flu for the season to date."