Parents are being urged to keep children at home if they are ill.
The call, from the Chief Medical Officer, comes as schools and childcare facilities reopen after the Christmas break.
The Chief Medical Officer says the re-opening of school and childcare facilities this week creates an environment for increased respiratory virus transmission.
Professor Breda Smyth says high levels of flu, Covid and RSV accounted for more than 1,200 hospitalisations last week.
She says this is placing significant pressure on healthcare resources, particularly hospital Emergency Departments and GP services.
Professor Smyth is urging parents to keep children home if they are displaying new symptoms of illness.
They should stay at home for at least 48 hours after their symptoms have fully or substantially resolved.
There is also an appeal to parents to consider the flu vaccine for their child which is a nasal spray that is free of charge by GPs and Pharmacists.
Prof Smyth says: "As schools and childcare facilities re-open after the Christmas break, I am urging parents to be vigilant for symptoms of respiratory viruses in children.
"If your child has any new-onset 'flu-like symptoms such as congestion, cough, runny nose or high temperature, parents should continue to be mindful of others and, if possible, keep their children at home from school or childcare facilities.
"Children should be kept at home for at least 48 hours after their symptoms have fully or substantially resolved.
"The vast majority of respiratory illnesses can be treated successfully at home with over-the-counter medication. There is very good advice on the HSE website undertheweather.ie. However, parents should trust their instincts and seek medical attention if required.”
"This year’s ‘flu season has not yet peaked, and there is still time for people to avail of a protective vaccine which takes two weeks to become fully effective.
"As we are still in the middle of ‘flu season, I am appealing to parents to please consider the ‘flu vaccine for your child. It’s a nasal spray and is administered free of charge by GPs and pharmacists."