It has always been the case that Ireland will have to 'step backwards' in the reopening plan if coronavirus gets out of control, according to a member of NPHET.
Professor Philip Nolan said officials have always stressed the need to move forward with caution.
He also said we're also likely to see "localised or regional-specific responses" to future outbreaks or clusters before the national response is escalated.
His comments follow a warning from the Acting Chief Medical Officer Ronan Glynn yesterday evening that the country's now in a 'precarious position' with the virus.
It also comes after phase four of the reopening plan was postponed.
Speaking on The Pat Kenny Show, Professor Nolan - head of NPHET's Epidemiological Modelling Advisory Group - said it's vital we keep the virus suppressed.
He said he has been "astonished" at how well the Irish people have responded to the pandemic, but the last few weeks have seen the level of COVID-19 begin to grow again.
He observed: "The plan was always clear: we needed to proceed with caution; that we could only go through the steps if the virus remains suppressed; and if we lose control of the virus, so to speak, we might have to step backwards.
"We have our mathematical models, we have much more knowledge of the virus than we had, and we have our statistical analyses. But the virus remains very unpredictable."
'I wouldn't use words like regional lockdown'
Professor Nolan said the 'upper end' of his group's current models is that there could be 150 COVID-19 cases a day in a few weeks' time - but said Ireland as a community has proven that we can suppress the virus.
He also said the virus' reproductive rate - currently estimated to be between 1.4 and 1.8 - becomes increasingly difficult to caclulate when the number of new cases is low.
He stressed that while a second wave could happen, we're in a "different position" now than we were before when we were caught by surprise.
In terms of the prospect of localised lockdowns like we've seen in Australia and England, Professor Nolan said: "Different types of outbreak and cluster - local, regional - are going to happen.
"I wouldn't use words like regional lockdown - I'd rather used words like localised or regional-specific responses to the problem at hand.
"Yes, in the future we may need escalating national responses, but before that we're going to need specific, public health led, risk-assessed local responses."
He said potential future measures include individual schools or groups of schools closing down, or restrictions introduced for certain types of workplaces.