The public has been asked to help prevent the spread of flu, as the latest figures show that it is now actively circulating in the community.
A total of 192 cases were notified in the week ending 20 November and 170 the week before.
There has been an increase in all age groups, but particularly in those aged 0-14 years.
Professor of Experimental Immunology at Trinity College Dublin Kingston Mills said after two years of having virtually no flu, we now have significant flu this season.
Speaking on RTÉ's Morning Ireland, he said that is not surprising as, due to pandemic lockdowns, the flu virus did not get a chance to circulate.
He said people in at risk groups are urged to get vaccinated against the flu.
"Unlike Covid, which is a disease that largely affects the older people, flu affects the very young and the very old or the immunocompromised, people on therapy for cancer or immune diseases so, younger people are at risk," Prof Mills said.
"And one of the ways of dealing with that is vaccinate both the children themselves two to 17-year-olds and is a very effective vaccine, which is given as a nasal spray. Very easy to administer and it is highly effective for that age group.
"But also pregnant women should get vaccinated, because not only would it protect the woman themselves, that could have a miscarriage if they got influenza, but it also protects the child because the child is very susceptible to infection, because it wouldn't have immunity itself yet and it gets that from the vaccine that's given to the mother."
Prof Mills added that it is very hard to predict the trajectory of the Covid pandemic and we are not seeing significant numbers of cases this winter.
"I think the risk of a twindemic is less likely now than people thought some months ago," he said.
"Ireland has very low cases, not zero, but very low cases of Covid.
"It has significantly more of a problem with RSV in young children and now with influenza. So, I don't think at this stage I can foresee there's going to be twindemic with Covid and an influenza," he added.
Flu is coming back with prevalence, he said, but for Covid is not and "is probably down to the fact that first of all so many people were vaccinated and secondly so many people were infected during the early part of this year".
"Omicron probably affected more than half the Irish population and the same across other European countries," Prof Mills added.
He said that those infections combined with the vaccine gives a high level of immunity in the population.
"It doesn't prevent necessarily the spread of the virus, but certainly prevents Covid-19 disease, especially severe disease, so that's probably having a significant impact.
"Of course, that is, depending on the fact that the virus doesn't change significantly again. And that that may still happen.
"So, it's really difficult to predict, but it looks good at this stage."