Professor Luke O'Neill says Ireland does now need to start reopening, and rapid antigen testing will be a "key weapon" to allow that to happen.
The Trinity College immunologist was speaking as NPHET and senior ministers prepare to meet this week to discuss easing the remaining restrictions.
The Government's due to announce a reopening roadmap next Tuesday.
It comes amid the ongoing Delta wave of COVID-19 infections, which has led to a significant increase in case numbers and hospitalisations in recent weeks.
Professor O'Neill told The Pat Kenny Show that the more transmissible strain of COVID-19 has certainly changed the situation.
He said: “Clearly the Delta is out there - that’s changed everything. We need to be a little bit careful, but we have to start reopening.
“My former colleague Paul Moynagh was saying this and I agree with him 100% - we need to get back towards things.
“We’ll need to observe certain things - we’ll have to wear masks indoors still, and antigen testing is a key weapon. They’ll still be in place for the foreseeable future.”
The live events industry is among the groups calling for wider use of rapid tests to facilitate reopening, although so far NPHET has been reluctant to give that the green light.
Professor O'Neill also said it was "slightly unnerving" to see large numbers of people not wearing masks while attending the All Ireland hurling final at Croke Park yesterday.
However, he said hopefully around 85% of that crowd (in line with the general population) will be fully vaccinated - therefore offering them a strong level of protection.
In terms of a booster vaccine campaign, Professor O’Neill said our surplus doses should be given away to developing countries before considering a third jab for the general population.
He said: “Give boosters to the vulnerable and the older people - the other people don’t really need a booster at the moment.
“Give that away to developing countries, and then come back [to the general population] next. That’d be the view of the WHO, which I would agree with.”
Earlier NPHET's Professor Philip Nolan told Newstalk Breakfast the Delta wave is unlikely to reach its peak until at least mid-September.
He said the vaccine rollout is going better than expected, but time is still needed to ensure more people are fully vaccinated - 7-14 days after their second dose.
He said there is now a need to come up with a plan to ease restrictions, but added that measures such as mask-wearing will still be needed as the reopening continues.