Professor Luke O'Neill says another vaccination campaign to protect against coronavirus is 'likely' in the autumn.
It comes as the number of patients in hospital with the virus has almost doubled over the past two weeks - going from 183 to 355.
However, the number of patients in ICU remains stable at 24.
Prof O'Neill, who is a member of the Government's COVID-19 Advisory Group (CAG), told Pat Kenny they are looking forward.
"The big question is come September/October will we see a big spike, because we're back indoors again - and this spreads indoors.
"CAG as it's called - the COVID Advisory Group - is very much planning for what's going to happen in the autumn.
"It's likely there will be another vaccination campaign, a fourth or fifth shot.
"It could be one of the newer vaccines because Moderna - just published yesterday - they've got an Omicron-specific vaccine that got a massive response in the trial.
"They're claiming an eight-fold improvement on their previous vaccine, based on measuring antibodies and so on.
"I'd like to see the data; but still, if that's true, that Moderna vaccine could be the one that we'll use in the autumn.
"It's the job of NIAC to advise on this, so they'll be looking at all this data".