There has been a huge surge in the number of cases of the common respiratory syncytial virus (RSV), which is putting paediatric hospitals under pressure.
The Health Protection Surveillance Centre has said it was notified of almost 1,000 cases of the illness last week.
It said 370 people were hospitalised, the majority of them children, and the peak has yet to be reached.
Up to 40 children a week have been admitted to the intensive care unit in CHI Crumlin since the beginning of November.
On one day last week, 39 children required ICU care, which is more than the number of beds in the unit.
Some children were treated in an overflow ward.
This has resulted in the cancellation of some scheduled surgery.
An RSV vaccine is expected for next winter, but in the meantime the HSE is encouraging people to get the flu vaccine, practice proper cough etiquette and mininise contact with others who are ill.
Speaking on RTÉ's Today with Claire Byrne, Consultant in Paediatric Intensive Care at CHI Crumlin Professor Suzanne Crowe said the numbers were similar to last year, but this year the surge looked like it would go on for longer.
"We have just received a lot of admissions over a very short period of time, so it has really got worse over the last two weeks all around the country," she said.
Prof Crowe said that GPs and paediatric units are seeing a large number of sick children.
"It is a very transmissible virus; it is spread from coughing and sneezing.
"It is droplet spread, and that is one of the reasons why we did not see it during the Covid pandemic because people were wearing masks and were staying away from each other," she added.
But now, she said, people have returned to pre-pandemic patterns.
Explore the Respiratory Virus Notification Data Hub.
— HSE Health Protection Surveillance Centre (HPSC) (@hpscireland) December 7, 2023
This week RSV remains at very high levels in Ireland. RSV is a common winter virus that causes coughs & colds. The highest rates are in babies & young children (aged 0-4)👉https://t.co/qSjINPMrqo pic.twitter.com/JWkbLmLrbV
Prof Crowe said children who are admitted would normally spend a week on the ward, while children in intensive care tend to stay on a breathing machine between three and ten days.
Regarding the cancellation of complex surgeries due to the uptick in RSV cases, she said they review the situation every day.
"We are doing everything we possibly can to get the cases done. So, each day we just look to see what resources we have available for that day, and we will try and do what we can," she said.
Prof Crowe said children during the first six months are most at risk of RSV.
"If you have a young baby at home, it is a worrying period," she told the programme.
Prof Crowe said there is a vaccine that some European countries have funded and are already using.
She added that the vaccine could be given to mothers towards the end of their pregnancy to give children immunity when born.
"The National Immunisation Committee has made the recommendation that it would be funded for patients in this country, and we are very hopeful that it will be," she said.
