Professor Luke O'Neill says booster vaccines are "like a refresher course for the immune system".
However, the Trinity immunologist says there's still debate around whether COVID-19 vaccine boosters should be rolled out this winter.
A number of countries are already planning to give vulnerable groups a third vaccine shot in the coming months, with Ireland also planning its own booster campaign.
However, the World Health Organisation has warned against a speedy rollout of third shots - saying the focus in the coming months should be on getting more vaccines to developing countries.
Research is also still ongoing into how long protection from the initial doses of the COVID-19 vaccines actually lasts.
Professor O'Neill told The Pat Kenny Show the question of booster shots is going to be a "hot topic" we'll be hearing more and more about in the coming weeks and months.
He said: “The question is when should we start to deploying them - or if to deploy them [at all]. The debate is still there at the moment - should boosters be used yet?
"The main issue being: should we not give vaccine supply to the developing world?"
Professor O'Neill said booster vaccines can "really get things going" after initial doses.
He explained: "It’s a bit like a refresher course for the immune system. The two shots get everything firing… but then things wane or perhaps gets less strong over time, so you give a booster.
"If you get a booster, you will get a really strong response. The prediction is that will protect you against any variant… and our fear is extra variants emerging.
“What we don’t know is how much the response wanes over time - that’s one slight unknown."
He said the evidence is growing, however, that boosters should be used.
Memory cells
Professor O'Neill explained it's not just antibodies that will reveal how whether the body is protected against COVID-19.
He said: “Even though the antibodies go down, the more important thing to measure is these so-called memory cells… there are loads of them in people post-vaccination.
"The big question is... will they persist over time? With some vaccines, they persist over years.
“Because it’s a new virus and we’re still learning so much, we don’t know exactly how long these memory cells will persist.”
For now, Professor O'Neill said there is some evidence of waning protection over time - particularly among those vaccinated earlier than others.
He believes many governments will “err on the side of caution” and go with booster shots.
The Trinity College immunologist stressed there won't be "endless boosters" - and scientists will be very closely monitoring how the immune system reacts to a third.
However, he suggested a third shot is unlikely to "overstimulate" the immune system, as doctors and scientists are now very aware of the right dosage to give when it comes to these vaccines.
