Professor Luke O'Neill says COVID-19 vaccine booster shots will be the "only way" to handle variants of the virus.
The vaccine rollout here is continuing, with 35-year-olds able to register for their jab from today.
However, while the initial rollout is set to continue through the summer and into the autumn, attention is already turning to the next steps.
It was reported last weekend that a vaccine booster campaign is already being prepared for the winter - likely involving single-dose Pfizer shots.
The preparations come amid the continued concerns over the Delta variant, and ongoing research to test whether vaccines are effective against it.
On The Pat Kenny Show, Professor O'Neill - Professor of Biochemistry at Trinity College Dublin - was asked by a listener if the Johnson & Johnson one-shot vaccine is effective against Delta.
He explained: “There’s evidence in the lab. They’ve taken blood from people who had Johnson & Johnson and then tested the antibodies. It is able to neutralise Delta.
“It is lessened - all the vaccines are slightly weakened in that regard. But still, Johnson & Johnson is driving an immune response in people that should protect against Delta.”
He noted there's not significant field data yet, as Johnson & Johnson jab has not been as widely used in the UK - where the Delta variant has spread rapidly - compared to other vaccines.
However, he said scientists are “confident” it does protect people from severe disease.
He said: “That’s the key metric - it doesn’t matter if you get infected really, as long as it doesn’t progress into severe disease.
“The only way to handle these variants is booster shots in the autumn - that will really kick off the immune system to protect against multiple variants.
“The way out of this variant issue is extensive vaccination now of course, but then also booster shots with any of the vaccines.”
Professor O'Neill also addressed the issue of antigen testing for large events.
It comes after the Government confirmed rapid antigen testing will be used for Ireland's first music festival since the pandemic began.
3,500 people are set to attend the festival, which will be held at Royal Hospital Kilmainham on July 3rd.
Professor O'Neill said it's "tremendous" that the tests will be used for the festival.
He said: “This is exactly what we want to see - any big event should really have antigen testing at it, and that’s going to happen. It’s a really good development.”
The leading immunologist suggested "we're going to see a lot more" rapid testing at such events, and we now "just need to get on with it".
He said: “It’s all the more relevant with the Delta variants.
"The antigen tests do pick up that variant - now we know that’s spreading in younger people, you can catch it through antigen testing."
He praised Denmark's handling of antigen testing, explaining: "If you look at the public messaging in [Denmark], it’s really good - the way they describe it, and the limitations.
"It’s not a magic bullet, and nobody ever said it was."