Professor Luke O'Neill says BA.2 is a COVID-19 variant of concern, but early indications are that vaccines should still offer protection against it.
BA.2 is considered a subvariant of Omicron and has been spreading rapidly across many countries in recent weeks.
As of last week, it accounted for an estimated 40% of current cases in Ireland - with CMO Dr Tony Holohan saying it could be the dominant variant here by the end of this week.
In a statement earlier this week, the World Health Organisation said BA.2 "should continue to be considered a variant of concern and that it should remain classified as Omicron".
They say the early evidence is that a previous Omicron infection should offer strong protection against reinfection with BA.2, while data reported so far have not indicated a difference in illness severity between BA.2 and the original Omicron variant (BA.1).
However, they to say it appears to be "inherently more transmissible" than BA.1.
On The Pat Kenny Show, Professor O'Neill - Professor of Biochemistry at Trinity College Dublin - said scientists are watching this variant closely.
He explained: “It’s like Omicron, basically - it’s a sibling of Omicron. They’ve renamed Omicron BA.1 because of the similarities between the two.
“Overall, so far it doesn’t seem to be that troublesome in that it’s similar to Omicron in how it causes the disease. But the prediction is it will be the dominant one.”
While scientists did consider whether to call this new variant Pi - the next letter in the Greek alphabet - they decided to keep it BA.2.
Professor O'Neill explained: “It’s quite different [to Omicron]... there was a slight concern that maybe it would have changed enough to make it more dangerous.
“So far what they’ve found - thankfully - in Denmark, the UK and South Africa [is that it's] causing the same level of disease as Omicron.
“But they’re watching closely. Certainly in unvaccinated people it would be a concern - maybe it would cause more severe disease, for example.
"It’s also more transmissible than Omicron… and Omicron itself was already highly transmissible.”
An early study from Denmark indicated that the vaccines were "slightly less powerful" against BA.2.
However, Professor O'Neill said the view at the moment is the weakening isn't strong enough to raise major concerns.
He said: “It’s kind of a mixed picture. Antibodies seem to be less against BA.2. But the other thing is they’re saying the t-cell part of the immune response seems to be holding up.
“That’s important because there will be more variants down the track. The fact we can still handle BA.2 gives us optimism that whatever variant comes up we should have some immunity against it.”
He added that antiviral treatments should also remain effective against this particular variant.