A new trial is expected to be run on the Oxford AstraZeneca COVID-19 vaccine after questions were raised about its performance.
The makers are applying for approval for the jab after tests proved it was 70% effective.
That jumped to 90% when an initial half-dose was given, followed by a full dose.
However, US scientists claim the higher rate of effectiveness only occurred in people aged 55 and under, and was discovered by accident.
It follows the announcement of a vaccine trial promising results by Moderna and Pfizer / BioNTech in recent weeks, with trials showing both vaccines to be over 90% effective.
Leading immunologist, Trinity Professor Luke O'Neill, does not believe that the issues over the AstraZeneca vaccine will affect it being approved in Europe.
Speaking on The Pat Kenny Show, he explained that it was a mistake that a lower dose of the vaccine was initially trialled which should make us "slightly concerned".
He said: "As ever, we have to see the data, what's frustrating here with all the trials is that we haven't seen any real data yet.
"This has certainly concerned people, but [AstraZeneca] told the regulator early on about the mistake and the regulator said keep going."
Professor O'Neill added that mistakes do happen in the development of vaccines, it just so happens in this instance that it is is very much "in the spotlight".
He said the good news is that the vaccine is working, and that a new trial is likely to happen soon.
He said: "They will re-run that trial probably now, and they'll do it upfront.
"They'll start with a low dose and then try a high and that can still give a 90% efficacy.
"They've also said it's unlikely to affect approval interests in Europe anyway.
"The FDA are the ones saying we don't like the look of this.
"The European agencies haven't said anything yet but AstraZeneca have said we're still expecting it to go down the approval route but time will tell."
The Pat Kenny Show
Professor O'Neill said AstraZeneca may yet get approval for its two high dose vaccine, which is 62% effective, but the question remains over whether regulators will require the company to do a re-test of its combined low dose and high dose formula.
He added: "The regulators are all over this and examining every bit of data, and now you can imagine the spotlight is on AstraZeneca.
"It will be up to the regulator to decide what to do next with this AstraZeneca trial."
He said he is waiting to see the publication of the data relating to all three vaccines so that "we can have a real go at comparing all three".
