A Professor of Experimental Immunology has said the whole population of adults, right down to age 19, needs to receive a booster shot.
Professor Kingston Mills of Trinity College Dublin he would not see any problem with giving vaccines before a five-month interval is up.
He said the benefits, on balance, would be to administer the booster jab now rather than waiting for a particular period of time, otherwise the risk of contracting Covid is higher.
Speaking on RTÉ's Today with Claire Byrne, Prof Mills said childhood vaccines are given at two-month intervals and there is no risk involved with receiving the vaccine before a five- or six-month period has passed.
Trials have shown that those who received a Moderna or Pfizer booster shot after the Janssen vaccine showed that booster effect was "tremendous".
People who received Janssen and AstraZeneca should be prioritised for a booster shot, once the other priority groups are completed, Prof Mills added.
Following that, he said, the rest of the population should get booster shots.
"There's no reason for leaving these vaccines sitting in freezers when people are getting affected and young people are getting affected now that they have been vaccinated, so why not boost them?"
Professor Mills also said antigen testing has a role to play. While it should not replace PCR testing, it could complement it in certain circumstances, he added.
The Chair of NPHET's Epidemiological Modelling Advisory Group has urged people not to delay or postpone appointments for taking booster vaccines, saying "every day matters when you pass that five-month threshold".
Professor Philip Nolan said the National Immunisation Advisory Committee (NIAC) is looking at whether to offer boosters to those under 50 years who got a Janssen one-shot vaccine.
He also said that if people followed advice on protecting themselves against infection, it would bring the spread of coronavirus under control.
Minister Heather Humphreys last night told a Fine Gael meeting that the country was currently capable of administering 220,000 booster vaccines a week. But, she said, work was under way to progress this to between 260,000 and 270,000.
Meanwhile, a school principal has said if authorities are serious about keeping schools open, teachers and SNA's should be prioristed for boosters.
Aidan Boyle, principal of Scoil Cholmcille in Ballybrack, said when teachers were out of school last year they were prioritised at number five on the vaccine list, but were moved to 13 when schools reopened.
"So I would feel that now we should be afforded a little bit of respect if we really are serious about keeping schools open, we need to prioritise boosters for teachers and SNA's," he said.
Mr Boyle also said there is not "a great deal of confidence" in the Minister for Education in how she has dealt with matters.
"Recently she denied there was an crisis of substitutes. That shows a very distant view of what actually happens regularly on the ground in schools," he said..
Mr Boyle said if the schools close there would be one million children at home and said he thinks the vast majority of the population would agreed that teachers should be prioritised to ensure schools remain open.
