HSE CEO Paul Reid has warned that the COVID-19 vaccine rollout is going to be a 'rocky road'.
He said the HSE can only offer 'uncertainty' at the moment due to the complications around vaccine supply.
It comes as the EMA will today decide on whether to give full approval to the AstraZeneca vaccine, including to over 65s.
An announcement is expected early this afternoon.
Mr Reid told Newstalk Breakfast we need to wait and see what decision is made, but there are many changing factors at play in the planning for the vaccination programme here.
He observed: “Where everyone is looking for predictability, certainty and clarity, all we can give at the moment is uncertainty."
The row between the EU and AstraZeneca over a shortfall in vaccine supplies has made headlines globally this week, but Mr Reid said some other European countries have also seen supply issues from other vaccine suppliers.
He also pointed to Germany, who've indicated they'll advise against the use of the AstraZeneca vaccine for over-65s as they believe there's not enough data.
While Mr Reid said there has been a rocky start in many ways, they'll be able to provide more clarity as the programme progresses.
He said: “This will get stronger and a bit clearer as more vaccines emerge.
"But we have to be frank and say we’re living with a bit of uncertainty for now."
For now, he said it's important to wait for the EMA announcement today, as well as waiting to see what emerges from the negotiations between the EU and AstraZeneca.
He said plans remain on track to vaccinate frontline health workers and care home staff and residents, and the take-up has been 'phenomenal'.
Mr Reid also said working through EMA and EU has “proven very beneficial for Ireland” during the COVID crisis and beyond, and the HSE wouldn’t want to damage those relationships by going through other channels.
He said he believes the current approach guarantees Ireland's the best supply of drugs for the future, although stressed any other decision would be down to Government rather than the HSE.