The HSE's hoping to start the booster vaccine process for over 30s by the end of the year, CEO Paul Reid says.
He says the timeline for the rest of the booster rollout is being finalised today, with details set to be announced today or tomorrow.
109,000 vaccines were administered yesterday, the second record-breaking day in a row.
106,000 of those were boosters or third doses for the medically vulnerable.
Mr Reid told Newstalk Breakfast the booster programme has been "rapidly accelerated".
He said: “We will be finalising today… details of the rollout for the rest of the ages.
“We do have around one million in those vulnerable groups, from the 40 years and over, still to do.
"So I would make a strong call to everyone… to please take up the first appointment you get.”
He noted that walk-in centres are also offering booster vaccines to over-40s, while people can also contact their local pharmacy to see if they’re offering boosters.
A HSE online booster booking system is also now available for several centres, and will soon be rolled out across all sites.
While many GPs have already started vaccinating their younger patients, the vaccine centres have so far only been offering boosters to over-40s.
Mr Reid says the HSE wants to make sure that the full booster process for 30-39-year-olds gets underway "before the end of the calendar year".
That's also likely to include anyone over 16 who previously received the one-dose Janssen vaccine, as they're set to be prioritised alongside the over-30s.
Yesterday, more than 6,300 new cases of COVID-19 were confirmed, with the five-day moving average having now risen above 5,700.
Mr Reid said the HSE's definitely now starting to see the impact of the Omicron variant.
He said: “There is no doubt what we’re seeing - particularly over the last 48-72 hours - is a higher number of cases beginning to take off.
“All indications from our [testing] centres is that they’re extremely busy.”
There's also high testing positivity levels, rising to more than 20% yesterday.
Mr Reid said it's clear we're now heading into an Omicron wave - and there's reason for both hope and caution.
He said: “There’s hopefully some emerging positive evidence around hospitalisations.
"But our concern is that while it may have a lower hospitalisation [risk] at an individual level, because of the volume of cases alone… that could have an impact on our hospitals.”
Mr Reid stressed it's still “really early days” in terms of evidence about Omicron.
However, he did note several recent studies have pointed to the efficacy of boosters against the variant and a possible reduced risk of severe illness compared to Delta.