Immunologist Professor Luke O'Neill has said 60% of COVID-19 cases in Ireland can be traced back to one strain of the virus in Spain.
Research from scientists in Switzerland suggests that a new variant of coronavirus - known as 20A.EU1 - appears to have cropped up in Spain during the summer and has since spread to multiple European countries.
The variant was first observed in Spain in June, and has been at frequencies above 40% since July.
It is also prevalent in the UK, Norway, Latvia, the Netherlands and France.
Prof O'Neill told Pat Kenny: "Last week it was first revealed that a strain of the virus emerges in Spain in around about June time, early summer.
"That has spread all over Europe and in Ireland, 60% of cases can be traced to that case in Spain.
"So again, it's evidence of travel between the two countries bringing this.
"In the UK it's 80% of the virus [that] came from Spain they reckon during the summer as well."
'Risky behaviour'
However the spread of this strain is not necessarily linked to the travel itself.
Prof O'Neill explained: "The viral count went down in Ireland, and to some extent other the parts of Europe, during the summer.
"And then it looks as if people go on holidays to Spain, and then the this particular strain is in Spain.
"And then people began getting infected in Spain, because, as the author's say, 'risky behaviour', hanging out together, the usual kind of socialising.
"And then they bring it back to their countries in Europe - and then this one then begins to ramp up.
"In other words, the strain that was in Europe at the time was low, this new one arrives and starts to spread again through this risky behaviour.
"So it's a really good example of how contagious this virus can be".
"The data in the UK: in mid-July, they lift the quarantine rule on people returning from Spain.
"And from that moment on, they begin to detect this virus in the UK population.
"So again it's evidence of spread, I guess, through behaviour being not not optimum on holidays."
Different strain
On the variant itself, Prof O'Neill said: "There's two options: either it is more transmissible, that's one possibility - and then begins to compete with the other one, spreads more readily, and then begins to spread in the population.
"They don't think so, though, they think it was to do with tourism, basically, and just just more people getting infected and bringing it to these countries around Europe.
"It could have come to Ireland from somewhere else in Europe, but it doesn't seem to be any more transmittable.
"They're blaming at the moment just just mixing and mingling - the usual things."
But he said this strain should have no implications for work on a vaccine.
"The changes are minimal because remember there's millions and millions of letters in the code for this virus - only six are different in this one.
"But again they're watching this closely, because obviously they keep taking samples from all over Europe and trying to track where the virus might be and what the strains might be, and is it changing?
"Obviously it's a big question to see if the virus is mutating.
"But at the moment there's no concerns with that.
"It just tells us again how travel allowed this to spread, I suppose, is the bottom line from this study."
Meanwhile keeping watered plants indoors could be a defence against the spread of the coronavirus.
Prof O'Neill said the next fight will be waged in the humidity levels of rooms.
He explained that viruses travel easier in dry air than moist air, and that is where house plants can play their part.
