Professor Luke O'Neill has described "heartbreaking" scenes on the Ukraine/Poland border after he spent the past week delivering supplies there.
The Trinity College immunologist is on his way back to Ireland and said he saw "unbelievable numbers" of refugees in Poland and Slovakia.
Speaking on Newstalk, Professor O'Neill said that starvation is a bigger worry to Ukraine at the moment than Covid-19.
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He said: "Only 30% vaccination rate in Ukraine.
"It was a country that had low vaccination rates, and that's the case in eastern European countries.
"At the moment I'm more worried about starvation, that's how serious it is there.
"But medical agencies are keeping a very close eye on Covid and other infectious diseases as well".
He described the scenes he witnessed while delivering aid to Ukrainian borders.
"We delivered a huge amount of medical supplies to the border with Poland and Ukraine - that was last Friday," he said.
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"And then we drove down to Bratislava in Slovakia [where] there's a huge depot run by Depaul, I'm an ambassador for Depaul by the way.
"They're coordinating a massive supply depot there.
"There's a lot of refugees, unbelievable numbers in Poland and in Slovakia, I couldn't get over it."
Professor O'Neill said there were no men to be seen among the huge numbers of refugees.
"We were in Krakow last weekend and the streets are full of families - we're talking mothers, grandmothers and children, no men. All the men are back fighting."
"Loads of Ukrainian number plates everywhere, same in Bratislava - we stayed in a hotel, there were 15 families in that hotel.
"It was medical supplies, food was needed because of the starvation happening, hygiene supplies - I was able to witness all that."
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