Professor Luke O'Neill says starvation - and not COVID-19 - is his biggest worry for Ukraine.
He is returning from the Ukraine/Polish border after delivering medical supplies as part of a convoy from Medical Help Ukraine - a group of Ukrainian doctors in Ireland.
The professor of biochemistry at Trinity College Dublin says they are now on their way back home.
He told The Pat Kenny Show what he saw.
"We delivered a huge amount of medical supplies to the border with Poland and Ukraine - that was last Friday.
"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.
"It was medical supplies, food was needed because of the starvation happening, hygiene supplies - I was able to witness all that."
He says the streets were full of families.
"There's a lot of refugees, unbelievable numbers in Poland and in Slovakia, I couldn't get over it.
"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's heartbreaking stuff... the kids especially are very traumatised and they're very disturbed by all this".
But Prof O'Neill says worries about coronavirus infection from all the movement is taking a back seat.
"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".