Vaccine registration should open for those aged 12-15 in the next two weeks, the HSE says.
They also say an estimated 10,000 people attended walk-in vaccine centres for their first dose yesterday.
The latest figures show 72.4% of adults in Ireland have now been fully vaccinated.
The rollout is now set to be extended to younger teenagers (aged 12-15) following a recent recommendation from NIAC.
Damien McCallion, the HSE's National Lead for the COVID-19 vaccination programme, told On The Record there's some work to do before that age group can register.
He said information for parents and children is being developed by NIAC, while the HSE's IT systems will also need to be upgraded.
He said: “Although we had a sense this was coming and we had started working on that, the systems were based on an adult-based [rollout].
“We would expect [registration] to open it within the next two weeks - we’d hope to announce the date this week coming. It will be a model where we’ll use the vaccine centres, but also GPs and pharmacies as well.”
Parental consent will be needed before younger teenagers get vaccinated.
Meanwhile, Mr McCallion said there was a huge uptake at yesterday's walk-in vaccination centres.
He said the figures are still being finalised, but "as much as 10,000” first doses may have been administered.
He noted: “Anecdotally, the feedback from our centres was there was a lot of young people but also people across other ages… who mightn’t have been able to take up [previous] opportunities.”
People on holidays within Ireland were also among those availing of the centres, and they'll now get their second dose at centres closer to home.
Mr McCallion said: “Overall, we’re very happy with how the first two days have gone.
"On Friday, we only had three centres operating - but there were very high numbers at those centres.
“It continues today and tomorrow, with over 20 centres open on both days.”
He added that scheduled vaccine appointments are now going out very quickly after people register online.
It has recently been confirmed that some people are receiving second doses of the Pfizer vaccine as soon as 17 days after the first.
That's despite the recommended gap being 21-28 days.
Mr McCallion assured people that it's “clinically safe and effective” to receive a second dose 17-20 days after the first.
However, he said the focus is still on sticking to a 21-28 day gap.