People who were due to be vaccinated later this summer may now be offered vaccines in July, according to the head of the HSE.
Paul Reid says a plan to accelerate the vaccine rollout has been submitted to Government.
It takes on board the latest recommendations from the National Immunisation Advisory Committee (NIAC), and would see the completion of the COVID-19 vaccination programme brought forward by a number of weeks.
As part of the proposals, 18 to 49-year-olds would have a choice of vaccine.
The official advice is those age groups should be offered an mRNA option - but can go for a dose of AstraZeneca or Johnson & Johnson if they want an earlier vaccination.
Mr Reid told The Hard Shoulder it would mean all vaccines could be administered quicker than anticipated.
"What would have potentially happened if we didn't have this option is we would have had a supply of Janssen and AstraZeneca that we couldn't utilise.
"So it does give us an option to utilise that now.
"What we've just briefed the Minister on... it does set out and does facilitate us bringing forward the completion of the vaccination programme by a period of a few weeks.
"Firstly it utilises Janssen and AstraZeneca supplies that we wouldn't have been in a position to do, and to start potentially vaccinating a lot of those people in July that would have waited longer".
Mr Reid says 45% of the population is now fully inoculated.
"We've always moved at pace with whatever supply that we have - so if you take it even just today, 4.17 million vaccines administered up to yesterday evening: 2.5 million dose ones and 1.7 million dose twos.
"So we now have 45% of the population fully vaccinated, 67% partially vaccinated.
"We're on a pace now which has always met every weekly supply that we get.
"It now becomes an even-increasing race to see whatever supplies that we have how we can utilise them."
He says new advice from NIAC, given on Monday, will see the rollout go even further.
"[This] gives options to use Janssen and AstraZeneca in age groups where it wasn't previously facilitated.
"What we have done with those recommendations is we have put together a plan in the last 48 hours - we've just briefed the Minister on it earlier today.
"We've fully embraced the recommendations from NIAC which... bring forward the AstraZeneca second dose now to four weeks - that was at one stage 16 weeks.
"We'd also be committing to looking to see how we give an option to those younger age groups to opt in for a Janssen or AstraZeneca."
But Mr Reid says one element that was dismissed by NIAC was mixing vaccine doses.
"That was considered by the National Immunisation Advisory Committee - they came down and said 'Not at this stage'.
"They're going to consider further evidence related to that, but they haven't recommended a mixing vaccines between dose ones and dose twos at this stage.
"But they're going to continuously monitor that.
"They'll give further advice on that, but for right now it's not part of their recommendations this week".