Around half of patients attending emergency departments around the country are turning up with the flu, according to the HSE.
The number of cases this flu season has already overtaken last year's peak, with 18 deaths reported so far this winter.
Visitor restrictions are in place for many public and private nursing homes, in a bid to limit the spread of the illness.
Flu season is expected to last for another month, and people are being encouraged to stay at home unless they need treatment.
The HSE has warned that venturing out to a GP or hospital is spreading the virus to more people, while also putting your own body under pressure.
Dr Vida Hamilton explained: "If you can have a normal conversation - that is you make sense and you're not confused - and you're able to take in fluids... then in general you're fit enough to stay at home and care for yourself with a flu-like illness.
"However, if you're very breathless; if you're confused or agitated; if you don't need to go to the loo despite more than 12 hours passing... then you really need to be seen by a health professional."
Health Minister Simon Harris, meanwhile, said it looks like the flu season has come to Ireland "much earlier" this year than in the past.
Health Minister Simon Harris says everything is being done to contain the spread of the flu.
New details from @HSELive show half of patients attending emergency departments are now turning up with the flu pic.twitter.com/uS0uwANmNY— Stephen Murphy (@StephenMNews) December 27, 2019
He explained: "It looks like it's come a lot earlier, and therefore it's likely to peak a lot earlier... and we would hope over the coming weeks to begin to see flu levels reduced in our country."
Anyone in at risks group - such as people aged 65 years and over or pregnant women - is also being advised to get the flu vaccine.
