Coronavirus vaccinations for over-70s may be delayed due to potential supply issues with the Astra-Zeneca Covid-19 vaccine, the Taoiseach has said.
Micheál Martin said a delay to the delivery of Astra-Zeneca would create a "real problem" for the rollout of the State's vaccination programme.
But he added that he expected "robust" discussions would be held between the European Commission and Astra-Zeneca in the coming weeks to try to solve the issue.
The British company has warned that supplies of its coronavirus vaccine to Europe will be lower than originally anticipated due to production issues.
Its vaccine is being rolled out in the UK, but the European Union has not yet approved its use. It is expected to make a decision on January 29.
Speaking on RTÉ Radio 1, Mr Martin said April, May and June were going to be "key months" in terms of the rollout of coronavirus vaccines, but that "the over-70s will be delayed because of AstraZeneca".
"Astra-Zeneca combined with extra volumes of Pfizer/BioNTech was going to be the catalyst for us to move from a low level of administration of vaccine to a mass vaccination situation," he said.
Despite the issue, the Fianna Fáil leader said the Government still aims to be in a "mass vaccination scenario" by the end of June.
He said the delivery of the Pfizer BioNTech vaccine had been on time and that there would be other vaccine deliveries.
But the Fianna Fail leader admitted that the supply of vaccines overall had been problematic.
"Our problem in January and February has been delivery - not getting enough vaccine into the country," he said.
"We had delivery of 150,000 vaccines up to the beginning of this week. By the end of this week we'll have 147,000, administered, so you can see there's very little in the tank.
"We're giving it out as fast as we get it in."
But he added that by summer Ireland would be in a "changed environment" due to large scale vaccination that will have been achieved by then.
Health Minister Stephen Donnelly described the Astra-Zeneca delay as a "real setback".
He tweeted: "The news from AstraZeneca, which has advised the EU of a reduction in vaccine supply in Feb and March, is a real setback.
"The numbers are still tentative and AstraZeneca is due to provide more exact figures at a meeting early next week. Will provide an update as soon as possible."
Up to January 20, some 121,900 people have been vaccinated in Ireland.
By Sunday, the Taoiseach said the majority of residents and staff of all long term residential facilities will have received a Covid-19 vaccine and that half of all frontline healthcare workers will also have received the jab.