The HSE admits the current flu jab will not fully protect against a new strain which is affecting people across the country.
It comes as the latest figures from the Irish Nurses and Midwives Organisation show 575 patients are on hospital trolleys today.
The new flu strain has surged and accounts for up to 60% of cases in some parts of the community.
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," said Dr Kelleher.
"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.
Dr Kelleher said: "We've been supported by the Department of Heatlh 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."