Overall influenza levels remain low, according to the HSE's Health Protection Surveillance Centre.
Its latest report for the week ending 4 December, says that influenza activity has started to increase.
Respiratory syncytial virus (RSV) activity remains at high levels.
RSV has also circulated earlier and at higher levels this season than normal and the number of admisisons is high.
Influenza-like illness rates are low in all age groups, however they have increased in all age-groups, except for the 5-14 year old age group.
The centre says that Influenza A (H3) is the predominant circulating influenza virus this season to date.
The Irish Pharmacy Union says pharmacists across the country are seeing a spike in respiratory and cold and flu-like symptoms in the last two weeks, as temperatures continue to fluctuate.
It is reminding people in the at-risk groups to get the flu vaccination.
The flu season lasts from October to April.
There are no reports of any influenza-associated deaths this season.
While influenza activity is increasing in some countries in the European region, overall activity remains low.