There has been a doubling of reported cases of influenza around the country in the past week, the new Health Service Executive (HSE) said last night.
The news came as overcrowding continued in accident and emergency units across the State, although the number of patients on trolleys has fallen.
The Irish Nurses' Organisation said some 254 patients were on trolleys yesterday, down from 422 on Wednesday.
It said the situation was worst at a number of Dublin hospitals and claimed there were 46 patients on trolleys at Tallaght Hospital, 28 at St Vincent's and 27 at the Mater.
Outside Dublin there were 15 patients on trolleys at Letterkenny General Hospital and a further 12 at the South Tipperary General Hospital in Clonmel.
The HSE said the number in the State had fallen to fewer than 200 by late afternoon.
The executive added that it was working on the €70 million 10-point plan approved by the Tánaiste and Minister for Health, Ms Harney, to alleviate pressures on the A&E departments. "While we would all like to see immediate solutions it will take some time to address all the capacity and other issues," a spokeswoman said.
Ms Harney was criticised by the Labour Party for not commenting on the A&E crisis. The party's health spokeswoman, Ms Liz McManus, said that at a time when the number of patients on hospital trolleys in A&E had reached record levels, the silence of the Minister was difficult to understand.
"We have not heard from Minister Harney on any health issue since before Christmas," she said.
The Department of Health said in a statement that Ms Harney was on a private holiday. "She will be returning to Ireland tomorrow. She has been in constant touch with her Department on a range of issues including the situation regarding A&E and is fully apprised of the situation."
Meanwhile, the HSE's director of population health, Dr Pat Doorley, urged anyone in a high- risk group who had not already received the flu vaccine to be vaccinated immediately, in light of the increased incidence of flu infection. Those in high-risk groups include the elderly, those whose immune systems may be compromised and those who suffer from chronic cardiac and respiratory conditions.
The HSE claimed the increased incidence of flu had been one of the factors which had added to existing pressures on hospital accident and emergency departments in recent days.
To date this winter, influenza activity, which is reported weekly to the National Disease Surveillance Centre, had been relatively low and there had been just one school outbreak.
Last year flu caused the death of one child and contributed to the death of another child, who was also diagnosed with meningitis.