The National Immunisation Advisory Committee (NIAC) 'may have to' revisit their decision to restrict AstraZeneca, according to a professor of immunology.
It comes as Johnson & Johnson delays the rollout of its COVID-19 vaccine in Europe.
The company said it made the decision 'proactively' after US authorities recommended pausing the rollout there.
The first doses of the one-shot vaccine were due to arrive in Ireland this week.
It also comes just a day after NIAC said the AstraZeneca drug should not be offered to people aged under 60.
Paul Moynagh is professor of immunology and director of the Kathleen Lonsdale Institute for Human Health Research at Maynooth University.
He told The Hard Shoulder one thing surprised him about the AstraZeneca change.
"Something that surprised me yesterday when it was announced - the recommendation - was that there didn't seem to be any consideration in terms of what effect this would have on our rollout.
"I was surprised by that, because when you're trying to evaluate the risks of these types of decisions and applying [the] precautionary principle - you have to look at the risks.
"And one of the risks is how does this effect the rollout? And how many people in the under-60s will be affected, how long will that be delayed by?
"That is part of your risk analysis, that needs to be an integral part of your risk analysis.
"A lot of this is managing risk, accepting that you're never going to get to zero risk.
"But a lot of this is evaluating risk and learning how best to manage it.
"I think we need to be careful in these situations not to apply the precautionary principle, and potentially mis-apply it, that we actually introduce higher risk - and potentially more damage - by applying the precautionary principle".
Asked by host Kieran Cuddihy if the Johnson & Johnson move meant NIAC should revisit their decision, Prof Moynagh said: "I think they may have to Kieran, because this appears to be an issue - these rare events - with these viral vector vaccines.
"If you look at Pfizer and Moderna, they are RNA vaccines, they're very simple vaccines... if you look at the Johnson & Johnson and the AstraZeneca they use a different approach.
"They basically take that gene that makes one of the viral proteins, and they put into another virus - an adenovirus - and there are different types.
"So these rare events, if it's proven to be the case, they seem to be associated with those adenoviral vectors.
"If that is the case again, and we apply the same approach as we did yesterday, that's going to have significant consequences in terms of our rollout over the next three months."
Prof Moynagh added that a target set to vaccinate 80% of the adult population within the next three months is going to be "a major challenge" if vaccines are left unused.
