The Chief Medical Officer is appealing to the public to get vaccinated against the flu and COVID-19.
Professor Breda Smyth has tweeted this weekend warning of an upsurge in cases of both illnesses in the past few days.
She is urging those with "any flu-like symptoms at all" to stay at home.
"With Christmas only one week away, we are reporting a significant surge in flu cases, up 80% on last week's numbers", she said.
"We have a number of patients in ICU with flu this week and unfortunately none of them have had their flu vaccine."
A flu vaccine can be booked at a GP surgery or pharmacy.
Ahead of the winter, officials were briefed that the health service faced a so-called ‘twindemic’ in which flu and COVID-19 cases threatened to overwhelm hospitals.
In addition, many people delayed accessing treatment during the pandemic, meaning there is a backlog of individuals with very serious illnesses.
Prof Smyth said that test positivity is now almost one in five, with 75 new hospitalisations each day with COVID-19.
#flu and #COVID19 cases and hospitalisations have increased. Please come forward for your #fluvaccine and #CovidVaccines. Please stay home if you have any 'flu like symptoms. pic.twitter.com/ianCv4UGv6
— Chief Medical Officer (@CMOIreland) December 17, 2022
"We all know that vaccination saves lives", she said.
"It decreases the chances of being infected and reduces the risk of severe illness from COVID-19 and flu, so please come forward and get yours."
Currently, the HSE is offering a third booster to individuals over the age of 65 or those over 12 who have a weak immune system.
Prof Smyth added that children appear to be particularly vulnerable to the virus, with them accounting for 60% of Australia's COVID-19 hospitalisations.
COVID-19 vaccine uptake
The HSE's Cheif Operations Officer, Damien McCallion, said that the organisation is “very concerned” about a lower than hoped for uptake of the COVID-19 vaccine in particular.
He told Newstalk Breakfast that the health service is “certainly under strain”, but the staff are doing their best.
“We’re seeing an increase in flu; it’s a little bit earlier this year", he said.
“We’ve a good uptake in terms of flu but we’re looking to encourage those people over 65.".
“[There’s] a much lower uptake on COVID and we’re really pushing hard for those people who are vulnerable and for healthcare workers - [it’s] really important in both the public and private sector that people get vaccinated. "
Main image shows sick cold woman next to a pharmacy. Picture by: Anna Berkut/Alamy