Chief medical officer Tony Holohan is warning that Ireland may face a wait for the first delivery of supplies of the new Moderna vaccine.
Around 880,000 doses of the vaccine are due here over the coming months and it is unclear how large the first shipment will be.
Dr Holohan said he does not expect the first delivery here to be as quick as with the Pfizer-BioNTech vaccine, supplies of which arrived from Belgium within days of approval by EU medicines regulators.
"I don't know if it will be as quick as with the Pfizer vaccine, where the supply followed in short order," he said.
The European Medicines Agency held an early meeting on Monday to discuss the Moderna vaccine and may recommend approval today. Its human medicines committee could issue an opinion on the vaccine from the US company and approve it after today's scheduled meeting.
Taoiseach Micheál Martin yesterday said around 75,000 people in long-term care and a further 60,000 healthcare workers should have received two doses of the vaccine by the end of next month.
He said there were high-level assurances from Pfizer to supply the vaccine here for the next two months.
There was good news yesterday that Pfizer and BioNTech could reach a deal with the European Commission to double the supply of their vaccine.
The bloc, with a population of 450 million, has already ordered 200 million doses of the Pfizer-BioNTech vaccine and has taken up an option to buy another 100 million.
Ireland is due to get 2.3 million doses this year. Everyone who is given the vaccine needs two doses.
Sources said the EU is seeking to buy 50 million or 100 million additional doses from the makers.
The new doses could be delivered between July and September, two sources said.
A European Commission spokesman declined to comment on numbers of possible orders.
However, on Monday he told a news conference the EU was trying to secure more doses from Pfizer and BioNTech in addition to the 300 million shots already booked
Meanwhile, Professor Karina Butler, chair of the National Immunisation Advisory Committee in Ireland, yesterday said that the rate of vaccinations in the first week of vaccination was deliberately slow as they wanted to ensure there were no technical issues.
Around 23 nursing homes are earmarked to share 3,000 vaccinations this week.
Dr Eavan Muldoon, a breastfeeding mother and infectious diseases consultant in the Mater Hospital in Dublin, was the first person to receive the vaccine among its staff yesterday.
"I wanted to demonstrate to mothers there is no reason to have concerns about receiving the vaccine while breastfeeding," said Dr Muldoon.