People are being advised to only go to Accident and Emergency Departments if necessary.
The flu season is set to be worse than last year with eight people having died so far due to flu related illnesses.
Both Donegal and Dublin are said to be the worst affected counties.
The HSE is advising influenza activity can circulate for a least the next eight to twelve weeks.
Older people are more likely to be affected.
The Assistant National Director of Public Health at the HSE, Dr. Kevin Kelleher, says most people can treat their symptoms at home:
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