Professor Luke O'Neill says modelling that led to indoor hospitality staying shut has to be looked at again.
It has emerged NPHET predictions of a huge COVID wave if indoor dining was allowed to go ahead did not account for new vaccine recommendations - allowing younger people to access AstraZeneca and Johnson & Johnson.
The models led to Cabinet deciding to delay the re-opening.
Prof O'Neill told Pat Kenny there needs to be clarity.
"It's just a bit strange in my opinion - if I'd have got the numbers, in science we need numbers, they gave us that range: 250 deaths or 2,179 deaths.
"There's a huge range there, you'd like to know which it's going to be.
"It's problematic as there's so many unknowns is the issue here really, that they try to take into account all the unknowns.
"But if someone in my lab came back with those two answers, I'd say 'Which is it?'
Here are the various scenarios NPHET presented the Government with for the spread of COVID over the next few months pic.twitter.com/uPgfxCaiXD
— Seán Defoe (@SeanDefoe) June 29, 2021
"You need to have a weighting on these numbers, if you can.
"I do have sympathy for them because there are so many unknowns really.
"The reason for this is there's too many variables that you can't control.
"A big one for me is this vaccination wasn't taken into account - that's got to be a key variable.
"So I'd like to see it re-run - I guess they're doing it now - to re-run the modelling with this new information on the vaccination programme.
"That's got to impact on the numbers, it should anyway, let's see if it does.
"It's important to find that out".
Prof O'Neill says for all the variables out of our control, there are other aspects we can control.
"There's so many unknowns here... there's some things we do know: we know how to mitigate indoors.
"Good ventilation, crowd control, time mitigates against risk of spread indoors.
"And I'm sure the hospitality sector and we can use all those measures and mitigate against the risk of this.
"And again, I wonder was that taken into account in a way that was fair - or did they say 'We can't trust the publicans to re-open safely', was that another factor that was put into the equations?
"My overall view is we have to learn to live with this virus, haven't we?
"And we know so much how to mitigate against it - I just don't see why they weren't a bit more, shall we say, prepared to look at the option of opening up indoors".
Health Minister Stephen Donnelly earlier told Pat Kenny : "NIAC (the National Immunisation Advisory Committee) provided that advice to the CMO on Monday.
"[The Chair of the NPHET Modelling Group] Professor Philip Nolan was having to do the modelling over the weekend.
"We asked NPHET to present to us several days early because the hospitality sector had very reasonably said, please don't wait until Thursday; it is not enough time so if there is bad news - and there was a growing fear because of Delta that there could be bad news - they said please give us this information as early in the week as possible. So, that is what we did."
He also said he was surprised to hear Cabinet sources claiming they thought the advice had been accounted for.