It's emerged this years flu vaccine won't fully protect against a strain of the virus.
It accounts for up to 60% of cases and comes as the latest trolley figures show 575 patients are waiting on beds in hospitals.
The HSE’s Dr Kevin Kelleher says it’s still important people get the vaccine:
"The B virus, generally speaking, produces a milder strain of flu for people."
"For a few younger people, it will cause really quite severe flu and cause them to be more likely to be admitted to ICU as a consequence."
He also says people with flu should not be in work: "We've been supported by the Department of Health and the Department of Education, as well as IBEC, in saying that if people think they have the symptoms, they should not go out."
"It is a very infectious disease, so if someone with flu goes into a workplace with 10 to 20 people there, five or six people will get flu."
The deadly 'Aussie flu' - also known as H3N2 - has already arrived in Ireland and is strengthening its grip.
The HSE revealed on Sunday that 'less than 10 people' in Ireland have already died from the so-called 'Aussie flu' outbreak .
The strain of the disease has affected up to 170K people in Australia - more than two-and-a-half times last year's total - with over 300 reported to have died.
Cases of swine flu and the B strain have also been detected in Ireland as experts say this year could see the worst flu epidemic since 1968!
A 'red zone' map showing where in Ireland is worst hit by the flu has been issued by the HSE.
The map - which covers all types of the bug including the deadly Aussie flu strain - goes from 'no report' to 'widespread activity'.
