Tánaiste Leo Varadkar has denied that delays to the rollout of vaccines in nursing homes has led to hundreds of deaths.
A total of 1,543 staff and residents in care homes have lost their lives during the pandemic - 369 of those coming in January alone.
This week, Tadhg Daly, head of Nursing Homes Ireland, criticised the rollout in nursing homes, saying just 10% of the initial 77,000 vaccinations administered by mid-January were in nursing homes.
On Thursday, Aontu leader Peadar Tobin said staff at nursing homes had told him that "the delay in the vaccine has led to hundreds of deaths".
Speaking during Leader's Questions, he said: "I'm not aware of so many people dying so quickly in any other institutions in the history of this state.
"The delay in the vaccine has led to hundreds of deaths is what I'm being told from the nursing homes."
Mr Tobin told the Dáil that at the Greenpark Nursing Home in Tuam, Co Galway, 35 of 49 residents tested positive for Covid-19 in the week they were due to receive the vaccine.
He said a fifth of those residents have now died.
He added: "In Blackrock Abbey, near Dundalk, 14 people have died, one man dying just a week after receiving the first dose of that vaccine.
"Nazareth House lost 11 people to Covid in two weeks. I'm told that the cemetery for those men that died in that in Nazareth House is akin to a war grave at the moment.
"These deaths happened just before the vaccine was to be administered."
Responding, Mr Varadkar said it was not possible to conclude that an earlier vaccine rollout could have prevented deaths.
He said: "We took a decision in this country to prioritise our healthcare staff and nursing home residents, and I believe that was the right decision.
"Bear in mind, it's only two or three weeks after you get the first dose that you get protection, and only two or three weeks after the second dose that you get full protection.
"I don't think you can necessarily draw the conclusions that you've drawn.
"But in terms of responsibility, the decision or prioritisation was made by the National Immunisation Advisory Council with support from Nphet.
"The practical rollout of the vaccine was carried out by the HSE.
"I think in fairness, the HSE have done a really good job. Once they got the vaccines, they got them out to people.
Mr Varadkar also said the rollout of Covid-19 vaccines to people over 70 "may well be slower" than originally planned.
It comes after the National Immunisation Advisory Committee (NIAC) recommended that people aged 70 and over should only receive mRNA vaccines - from Pfizer/BioNTech or Moderna - where possible.
It means the AstraZeneca vaccine will now be given to healthcare workers and vulnerable people under the age of 70, Mr Varadkar told the Dail.
Mr Varadkar said he could not give exact dates for the new rollout schedule but confirmed it would take longer than planned.
On Thursday, Minister for Health Stephen Donnelly said he has signed the authorisation for use of the AstraZeneca vaccine.
Mr Donnelly said it will be used by Ireland's vaccinators immediately.
"The first delivery of this vaccine is due next week," he tweeted.
"Ireland now has three safe and effective vaccines."