Unvaccinated people are having a 'disproportionate impact' on the health service.
That's according to the HSE's Chief Operations Officer Anne O'Connor.
She was speaking as there were 415 patients in hospital with the virus on Thursday – a 17% increase on last week.
There were 70 in intensive care, which is one more than last week.
While the number of COVID-19 patients being admitted to hospital has increased by 43% in the past two weeks.
There are an average of 50 COVID-19 admissions a day at the moment, compared to 35 at the end of September.
While there are five admissions to intensive care per day.
Ms O'Connor says it is largely down to 370,000 adults not being fully vaccinated.
"Those, I suppose, 10% of the adult population is driving 50% of our admissions.
"So it's a disproportionate impact in terms of the people who are unvaccinated presenting.
"Unfortunately that is still a significant number for us.
"Having 70 people in our ICUs who are COVID positive puts a very significant demand, and the fact that three-quarters of them are unvaccinated equally is of significant concern".
And she says there is also increased demand for non-COVID care.
"We are seeing very significant numbers coming forward for care; we're also seeing quite a high level of admission - and that is a changing picture in recent weeks.
"We have averaged over the last eight weeks about 6,000 admissions - in the past week that's gone up to about 6,500.
"So we are seeing sicker people, frailer people coming forward who are in need of hospital services.
"So I think the burden comes from having to provide services to everybody".
It comes as Government ministers insisted they still aimed to push ahead with the planned re-opening next week - but will have to listen to the advice of the National Public Health Emergency Team (NPHET).
Foreign Affairs Minister Simon Coveney said the recent increase in COVID-19 cases was a 'warning shot' that may see some restrictions remain after October 22nd.
While Finance Minister Paschal Donohoe said a decision would be made next Tuesday, noting that he wanted to avoid any situation where restrictions would have to be re-imposed.
And Taoiseach Micheál Martin urged people to "knuckle down" and follow public health restrictions, while the Higher Education Minister Simon Harris suggested the use of vaccine certs could be extended.
Additional reporting: Eoghan Murphy