Chair of the Covid-19 vaccination taskforce Professor Brian MacCraith has said it remains "very cautious" on specific targets given the recent setbacks with supply.
Speaking on RTÉ's Brendan O'Connor, he said he has counted more than 15 changes to supply since he started in his role on the taskforce so that shows the level of uncertainty around it.
"This is all about hope and managing the expectation" he said.
He said the plan is that over 70s will have the first doses of the vaccine starting on Monday week (15 February) with that completed by mid-April, which is a couple of weeks later than planned.
He said that is because two vaccines are now being used instead of the planned three, with AstraZeneca not advised for this age group.
He said the details of this plan are very positive news for the over 70s and they will be contacted by their GPs in the next week or two.
He said after their first dose is administered they can expect the second one to be given by early to mid May.
He said this week they will be looking at vaccination centres where some of the over 70s' patients will be receiving theirs instead of at their GP practice.
The overall focus is to administer vaccines as soon as they arrive in Ireland and it is "completely supply driven," he added.
Mr MacCraith explained how by last weekend just under 200,000 vaccinations had been administered out of a total supply of 207,000 that had arrived in Ireland,
He also warned that any missteps in the early stages of a vaccination programme can cause uptake rates to fall.
Speaking on the same programme Dr Nina Byrnes, a GP in Castleknock in Dublin, said there is a lot more information that GPs require before the vaccination rollout on the over 70s starts from 15 February.
"We need concrete information and when we are getting them, as people are waiting," she said.
The logistical challenges are quite different between Pfizer and Moderna vaccines and they would like to know which vaccines they are getting for their patient as there are huge differences in how they are dispensed and administered, she said.
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Meanwhile, preparations are under way for the inoculation of thousands of healthcare workers against coronavirus infection from tomorrow.
They will be injected with the AstraZeneca vaccine, 21,000 doses of which arrived from Belgium yesterday.
The consignment was delivered to the Health Service Executive's cold chain store in Dublin.
AstraZeneca decision not logistical but clinical - Reid
Chief Executive of the Health Service Executive Paul Reid has said there will be three GP-led vaccination hubs in place from next week with a further plan for 40 vaccination hubs around the country at a later stage.
Speaking on RTÉ's This Week, he said "significant progress" has been made on the plans and also in terms of the workforce needed for the 40 hubs.
Of the 1,300 GP practices around the country, he said 900 practices will carry out vaccinations from Monday week as the vaccination of the over 70s begins.
He said for patients of other practices they will travel to the three centralised vaccinations centres based in Cork, Galway and Dublin and there will also be buddy-up systems between some practices with smaller numbers of patients.
Mr Reid also moved to reassure those in remote areas who are housebound that they will not be left behind.
Referring to the decision not to use AstraZeneca on the over 70s, he said it is not a logistics issue but a clinical decision.
He said the the vaccine that has the most data and deemed the safest is being used for that particular age group.
He said the Pfizer and Moderna vaccines will be used to protect the most vulnerable in the over 70 group.
Mr Reid said he is quite confident that there will be "more predictability" around vaccine data as they are rolled out on a higher level in the second quarter of this year.
"What we have always said is whatever vaccine is approved for whatever cohort and whatever supply we get we will use. That has been our experience to date".
He confirmed that the first dose among the over 70s should now be completed by mid-April instead of the inital target of the end of March, while the second dose will be administered in May.
Mr Reid said they have seen some relief in the hospital systems this week but warned we "are a long way from being out of the woods".
He said the number of people admitted to hospital with Covid-19 is still 50% higher than at the peak of the first wave in April last year.
He said 1,208 people are in hospital with the coronavirus and 178 of those in ICU.
McDonald urges spirit of 'generosity and solidarity' on vaccine sharing
Elsewhere, Sinn Féin Leader Mary Lou McDonald has said the UK should share any spare coronavirus vaccinations with Ireland.
Ms McDonald said a spirit of "generosity and solidarity" on vaccine sharing should extend globally.
She was asked on Sky News if she would like to see excess UK doses being diverted to the Republic, given the slower pace of vaccine rollout in the EU.
"Certainly if there is an excess of supply in Britain and if there is a capacity for that to be shared with Ireland at some point, well, yes, of course, absolutely, the project here is to get people vaccinated," she replied.
"This is a race against this virus and against death so, yes, I think a spirit of fairness and generosity needs to prevail in this, my goodness, above all other issues.
"So, yes, is the answer, and if the scenario were vice versa I would expect that a similar generosity would be afforded to the British people because the virus doesn't care about politics or borders or any of these things."
"We all share the same human biology and it's just so important that the incredible work that has been done by scientists internationally, including at Oxford University, and across the globe, that the fruits of that endeavour and knowledge and expertise is shared in the way that good science would intend, and that means keeping all of our fellow human citizens safe and alive and well."
