Professor Luke O'Neill has said Ireland should be aiming to vaccinate every citizen by the end of June.
The Trinity College Dublin immunologist said we should be following Denmark's example.
He was speaking after the European Medicines Agency (EMA) said the single-shot Johnson & Johnson vaccine could be approved by mid-March.
Ireland has an Advance Purchase Agreement for 2.2 million doses of the drug.
Prof O'Neill told Pat Kenny if the supply chain holds, Ireland needs to be more ambitious.
"Denmark - who are like us remember, they're depending on the EU, they say they'll have all their people done by June 27th - which is well ahead of us.
"Why can't we be like Denmark, is the question.
"They have said 'look that's our ambition, we need the Johnson & Johnson vaccine to make sure we get to that point and then we need to make sure the supply of the others keeps coming up'.
"So they've said it could be delayed, but the only thing that should stop us now is supply.
"Nothing else should be a variable here of any kind.
"In other words as soon as we get the vaccines in, get them into people's arms.
"And we should be like Denmark: I'd love it if our Minister for Health said 'our goal is June 27th just like Denmark to have our whole population vaccinated'.
"In fact the Danes said this just before the summer holidays as a way to cheer people up, I suppose.
"But it does depend on Johnson & Johnson, there's no doubt."
'Ireland should be aiming for that'
However Prof O'Neill said the supply chain can be predicted to a certain point.
"They can kind of project the supply chain anyway, because... Pfizer, AstraZeneca and Moderna have told them how much they can give them.
"That might fall down - as we've discussed before things can go wrong and the factory can shut down for some unknown reason - so there are unknowns there.
"But certainly if the supply is as they say it should be with Johnson & Johnson as well, the Danes have said June 27th - I think we should be aiming for that as well."
If the EMA concludes that the benefits of the vaccine outweigh its risks, it will recommend granting a conditional marketing authorisation.
The European Commission will then issue a decision on whether to green light it in all EU states 'within days.'
Johnson & Johnson is the parent company of Janssen, both of which have Irish operations.
It is the fourth drug to be put forward for approval - following BioNTech/Pfizer, Moderna and AstraZeneca.
The Janssen vaccine only requires a single dose to be effective, unlike all others approved so far, and can be kept in a standard fridge.
While recent data also shows that the Pfizer-BioNTech vaccine can be stored in 'a regular freezer'.
Until now, the drug had to be kept at ultra-low temperatures of between -80°C and -60°C
It comes after the two companies asked the US Food and Drug Administration (FDA) to relax requirements for their vaccine to be stored at these temperatures.
