More than half of people admitted to intensive care units between July and November were unvaccinated.
According to the Central Statistics Office's Covid-19 Insight Bulletin, unvaccinated people accounted for 54% of Covid-related ICU admissions over the last five months.
More than 9-in-10 (92%) also reported having an underlying health condition.
The median age of the unvaccinated patients who had contracted Covid and were admitted to hospital between July and November was 38 years.
The median age for vaccinated patients was 66.
Nationally, almost two-thirds (59%) of those admitted to hospital under the age of 24 had not been vaccinated against coronavirus.
The equivalent figure for those aged between 25 and 44 was 48%.
The average hospitalisation rate has stayed below 30 people per 1,000 confirmed cases since April.
At the same time, the average ICU admission rate has been less than five people per 1,000 confirmed cases.
Further analysis found that, of those admitted to ICU who contracted the virus between July and November and who were not born in Ireland, 84% reported being unvaccinated, compared to 41 for those born in the state.
Between September and November, Ireland increased its vaccination uptake by just under 3% - higher than the average increases reported in the UK and the rest of the EU.
The CSO bulletin also included a detailed breakdown of the overall vaccination uptake to date among people living here.
In Ireland, more than 9 in 10 Local Electoral Areas (LEAs) had a vaccination uptake rate among over 12s of at least 83.7%, up to November 11.
The majority of LEAs in the lowest category of vaccination uptake rate — below 83.4% — were located in Dublin: Clondalkin, Tallaght South, Lucan, Blanchardstown-Mulhuddart, Ballymun-Finglas, Ongar the North Inner City and the South-West Inner City.
Outside the capital, only Killarney, Carndonagh, Lifford-Stranorlar, Buncrana, Cavan-Belturbet, Monaghan, Carrickmacross-Castleblayney, and Dundalk-Carlingford within this category.