There has been a rise in cases of influenza and high levels are expected between Christmas and the New Year, according to interim Chief Medical Officer Professor Mary Horgan.
Notified cases of influenza increased by 67% to 277 in the last week.
Prof Horgan said the incidence is highest in those aged one to four years, followed by those aged 80 and older.
Last week, 73 cases were hospitalised, compared to the previous week.
Prof Horgan has urged people to avail of the free flu and Covid-19 vaccines from participating GPs and pharmacies.
The uptake of the nasal spray flu vaccine for children is currently at just under 16%.
Among adults over 60 years, the uptake for the flu vaccine is over 58%.
The uptake of the Covid-19 booster is highest in the over 80s at 56%.
The number of people vaccinated against flu and Covid this year has passed 1.5 million, according to the Department of Health.
Prof Horgan said that the impact of the Respiratory Syncytial Virus immunisation which began on 1 September for newborns is already being seen with much fewer cases.
Just 23 cases have been reported this year, compared to 496 for the same period last year.
Hospitalisations are down to just 13 compared with 316.
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Speaking to RTÉ's News at One, Prof Horgan said that in the past two weeks, there has been an increase in flu being diagnosed in the community.
"When we see it above a certain level, we assume that there is widespread community infection with influenza," she said, adding that while over a million vaccines had been administered, the uptake could be better.
"Particularly coming into the Christmas season; we anticipate that there will be a peak after Christmas, probably early in the New Year.
"We all like to spend time with our family and friends over Christmas. There is a lot of intergenerational mixing, and what we want to really do is avoid people being sick or indeed hospitalised over Christmas."
