The HSE has told GPs that vaccinators may not receive their full orders of Covid-19 vaccines in the coming weeks, due to a new shortage of supply.
It said the number of doses available is slightly less than previously advised, due to an issue with the delivery of Moderna vaccine.
The HSE said the available supply is about 15% less than the required amount to vaccinate the entire over-80 population.
However the health agency has said the shortfall will be made up in a few weeks time, and there will be a huge ramp-up in vaccine delivery in April.
The HSE updated GPs of the problem in an email last night.
Another vaccine supplier, AstraZeneca, has struggled to meet its delivery targets to Ireland but has committed to making up the shortfall according to the head of the HSE Paul Reid.
Supply issues with about 70,000 doses forced the health service to wind down its target number of jabs administered for last week.
It has set a target of 84,000 this coming week and plans to begin giving the over-80s group and medically vulnerable group their first dose.
Mr Reid said this quarter of the year has been challenging because of unpredictable vaccine supplies from pharmaceutical companies.
"Ultimately what we have been committed to for this quarter from the three suppliers, Pfizer, Moderna and AstraZeneca, is a total delivery of just about 1.2m [doses]," Mr Reid said.
"However, we have always said that almost 200,000 of those are due to arrive on the very last day of the month March 31, so it is almost impossible to vaccinate those on that day.
Meanwhile, GPs are rep[orting that vaccine take-up remains high in the over-80s population.
Speaking to Newstalk this morning Donegal GP, Denis McAuley, said no person called for a vaccine dose has turned down an appointment yet.
"Nobody has refused the vaccine in my practice and I have not heard of anybody refusing the vaccine so far. Which is wonderful," Dr McAuley said.
"I think this is a group that is well informed and they know the risk-benefit analysis means that it is, without doubt, the most sensible thing to do.
"Hopefully that attitude will continue down through the cohorts even below the under-70s," said Dr McAuley.