With the Omicron variant now accounting for 11 per cent of Covid-19 cases here compared to less than one per cent just one week ago, according to Chief Medical Officer Dr Tony Holohan, the next two weeks will be crucial for the booster campaign.
"If there's nothing else that we do in the next 10 days before Christmas, everything has to go in to maximising the number of boosters that we get into arms in the next two weeks,” Professor Christine Loscher told Newstalk Breakfast.
"Omicron has accelerated much more quickly than we thought, and we do know that that third dose is vital to controlling case numbers.
"And I think we'll see that that 11 per cent is going to climb very quickly in the next week or two.
"We will definitely have dominance in the next 10 days.
"We don't know enough to not be concerned - but I think there is good optimistic data that it may be milder, and that may be a good thing for us".
Yesterday, Health Minister Stephen Donnelly said the wait time between a second Covid-19 vaccine and a booster has been reduced from five to three months, following new NIAC advice.
Up until now, people vaccinated with anything but Janssen had to wait a minimum of five months after being deemed fully vaccinated before getting their booster.
Professor Loscher said that shortening the booster waiting period makes sense.
"I think it's really significant - it comes off the back of the head of vaccine strategy of the EMA, recommending that the booster interval be lessened,” she added.
"We're responding to the acceleration of Omicron, where we know that booster dose is absolutely vital.
"And the second thing is that new science has come to hand where this... study in the UK has shown categorically that after two weeks, you get as good a response with the booster as you would a few months later.
"So I suppose its allowed us to be able to really lessen that interval, without having a huge impact on losing any of the benefits of boosting".
Prof Loscher believes it is right to boost older people - and those with underlying issues - first.
"Coming down through those cohorts in the way that we did before is sensible; but the people who got J&J [Janssen] - we know that their immunity has waned much faster and is much, much lower.
"So I think they should be prioritised, regardless of age, and that is the one cohort I think we should focus on".
She says this one-shot vaccine was one of the first offered in pharmacies.
"It was one of the first ones made available through the pharmacies, and a lot of young people took it - it was a single shot.
"But I suppose the science has moved on now and we know now that that has waned the quickest in terms of immunity.
"So I really think that they need to skip that age queue."