The global coronavirus vaccine rollout is set to be "the most amazing event in the history of human health", according to Professor Luke O'Neill.
The Trinity College immunologist says Ireland's now expecting to get nine million doses of the virus - enough to vaccinate everyone in the country.
As regulators start the approval process for several promising vaccine candidates, authorities - both national and international - are starting to plan for how approved vaccines will be rolled out.
Ireland is bidding for supplies through the EU, with the European Commission placing orders with five vaccine makers.
Some vaccines - such as the one being developed by Pfizer - need a double dose, meaning double the amount of doses are needed to inoculate everyone.
Meanwhile, global initiative COVAX is working with vaccine manufacturers and dozens of governments to ensure no countries are left behind in the process.
On today's Pat Kenny Show, Professor O'Neill said COVAX is a "remarkable organisation".
He said: "90 governments have put money into COVAX. Its job is to vaccinate the poorer countries and the middle income countries... we must vaccinate them as well.
"Poor countries always do worse in a pandemic for all kinds of reasons. There [also] wouldn't be any point in vaccinating Europe if we aren't vaccinating other parts of the world - it could always come back in."
Professor O'Neill said we're looking at the "largest and most rapid vaccine deployment strategy in human history".
He noted: "The logistics are all being worked out. We're going to see the most amazing event in the history of human health, in many ways - can you imagine the goal is to vaccinate seven billion people in the coming months?
"It's a really good example of countries mobilising together."
In terms of Ireland, Ireland is likely expecting vaccine supplies from two or three countries.
Professor O'Neill said the process could start in the first couple of weeks of January, but it will of course "take a few months" to start rolling out to the wider population.
Situation in America
Professor O'Neill also spoke about the worrying situation facing hospitals in the US at the moment.
He told Pat: "Several hospitals in America are now begging for more staff, and the frontline is under severe pressure.
"The evidence is really clear now that America sadly is in trouble. Governors are now issuing mask mandates and calling for restrictions... at last."
He explained that Texas is seeking thousands of extra healthcare staff, while Tennessee and Virginia are very close to having maximum capacity.
He said: "Some of the commentators in America are saying 'how could the richest country in the world be rationing healthcare in several states?'
"They have to triage much more aggressively. Some people are not getting treated, because there's not enough capacity."
He said the situation means there's now a "massive spotlight" on the American healthcare system - and that they're now getting ready for a potential post-Thanksgiving surge.
Professor O'Neill said Thanksgiving is a 'repeat' experiment, after Canada saw a spike in cases following their own Thanksgiving holiday.
He suggested Europe needs to look very closely at what happens in the US over the coming weeks as we prepare for Christmas.