Professor Luke O'Neill says Ireland is very close to defeating the spread of the coronavirus in the community.
He told The Pat Kenny Show: "We're almost there - we're tantalisingly close, Jonathan, that we're going to nearly get elimination in Ireland.
"It is the question of the all-Ireland policy, the travel is the big bug-bear isn't it?
"We're pretty close to this now.
"The next issue's going to be the dreaded pubs again, isn't it, on August 10th so what do we do then?
"But we're very close to being in a much better place than we've been - so in other words we can be somewhat optimistic.
"But again it's vigilance and everybody has to keep doing the same thing, it's like a mantra at this stage isn't it.
"If we keep doing what we're doing we'll keep this thing at the level it should be is the idea."
Asked about upcoming plans to re-open schools next month, he said: "It would help if they wear masks wouldn't it?
"It's another weapon to use".
"I think it would be a good idea if secondary school students wear masks, certainly if they can't socially distance properly.
"In a classroom that's well ventilated they can stay apart, then the need for a mask is slightly less.
"So I guess it could be depending on the local situation.
"But masks will definitely help".
"It's all about those dreaded numbers, isn't it - every night we listen to the number.
"If they begin to go up then you can't open the schools or you have to re-close them, so lets keep our fingers crossed".
"One case in a school, that might then start spreading you see.
"But we do know if you observe all the guidelines, and we know they're working very hard in getting the guidelines to be as perfect as possible, that's the thing to do.
"That means that it's unlikely that schools would become a source, but you need to have all these measures in place."