More than 869 people were in hospital with flu as of this morning, according to the HSE.
That total is a rapid increase from the 530 people hospitalised with the condition as of last Sunday.
On Friday, there were 742 people admitted, which increased to 809 on Saturday.
HSE chief executive Bernard Gloster said the HSE expects the numbers to rise to around 900 in the coming days.
“We are taking several measures to prepare for the potential surge in hospitalisations and intensive care admissions due to the flu,” he said.
“The intensive care capacity is currently managing, with 323 available beds and 300 people in ICU, though not all of them are flu cases, but the flu adds pressure to the wider system.”
Between December 20 and 27, some 34,400 people attended emergency departments, which was an increase of 27,800 for the same week last year.
Some 8,500 patients were admitted compared to 7,800 for the same period yet there were — according to the HSE — fewer people on trolleys.
Mr Gloster added: “Record discharges over the course of this seven-day period is keeping the system to some degree stable.
“The overall patient flow system is moving better than last year, and the healthcare system is focusing on every lever to keep the patient flow system moving and keep everyone safe.
“To respond to the increase in demand, the healthcare system has ramped up measures in the community, including longer GP opening hours and increased out-of-hours services.”
The HSE has urged people to stay at home if they have flu symptoms.
“Seek treatment from the pharmacy, your GP, GP out-of-hours, and injury units for non-life-threatening conditions such as fractures and burns,” a spokesperson said.
“Please cooperate with our staff should hospital visiting restrictions be in place due to flu and other circulating infections, and continue to practice infection prevention measures such as handwashing and covering coughs and sneezes.”
They added: “The HSE urges anyone with breathing difficulties or chest pain to attend the emergency department for treatment or call 112/999 in an emergency, and patients with non-life-threatening conditions should seek healthcare in the community.”
There are pharmacies giving flu and Covid vaccines all over the country.
Details of where they are and how to book an appointment near you can be found at https://www2.hse.ie/services/pharmacies-flu-and-covid-vaccines/