A mandate on mask-wearing should be kept on public transport, according to Luke O'Neill.
The professor of biochemistry says buses and trains are the 'perfect place for the virus to spread.'
He was speaking as the National Public Health Emergency Team (NPHET) meets to consider lifting the legal requirement for face masks to be worn in certain settings.
But Prof O'Neill told The Pat Kenny Show keeping masks in certain settings makes sense.
"I'd mandate them on public transport for definite.
"We know from other studies years ago: you mainly catch colds and flus on public transport in winter cause you're crammed in together.
"One reason why flu went down, we think, is less people were on public transport and we were wearing masks.
"Public transport - enclosed space, very stuffy - perfect place for the virus to spread.
"So I'd certainly maintain mask-wearing on public transport.
"Other settings it'll have to become optional - I mean we can't have laws about everything, can we?"
But he says any change to the mask mandate should not be during flu season.
"My other concern is we're still in the middle of winter, remember.
"I think they should maybe leave it a few weeks really until the winter's passed.
"The virus is still rampant out there - it makes sense to me to leave it a few more weeks.
"It looks like they're going to lift the mandate.
"Remember they recommend we should wear masks anyway - we should keep wearing them".