Record numbers of people have been attending their GPs with flu-like illness over the past week, according to the National Disease Surveillance Centre (NDSC).
The centre, in its latest weekly flu report, said the GP consultation rate for influenza-like illness over the past seven days reached the highest recorded levels for this period since its influenza sentinel surveillance scheme began three years ago.
Under the surveillance scheme, more than 30 GP practices are asked to provide weekly returns on flu activity in their area. Almost one third of them reported flu activity in the past week with the majority of cases being reported in the east, south- east and south of the country.
The bulletin states that influenza A is now circulating in Ireland, north and south, and the NDSC has urged people to get the flu vaccination. It is free to people over the age of 65.
"Although laboratory confirmations of influenza virus started earlier this season than previous seasons, it is still too early to predict whether this early activity will be sustained," the NDSC report said.
Three schools have already closed since September due to flu outbreaks. These included Naas CBS in Co Kildare; St Columba's boarding school in Rathfarnham, Dublin; and Scoil Cormac in Cashel, Co Tipperary.
The Eastern Regional Health Authority's director of public health, Dr Marie Laffoy, has also urged people in "at risk" groups such as the elderly and those with heart conditions or asthma to get vaccinated. She said it was a worry the illness had occurred so early in the season and it was very possible there would be increased influenza activity for the rest of the year.