Ireland having over 500 coronavirus cases a day 'considerably narrows' the options for easing restrictions, the HSE's Dr Colm Henry says.
He says the recent increase in daily figures is disheartening, but there is also cause for 'great hope' - saying the country is 'not back at square one'.
NPHET last night reported 769 new cases of COVID-19, while the five-day moving average is now over 580 cases.
HSE CEO Paul Reid has also voiced concern about the increase in COVID-19 hospital admissions over the weekend.
On Newstalk Breakfast, Dr Henry said there's 'no doubt' it's a frustrating time.
He said: "It’s disheartening to see those figures go up again.
“We’re not really seeing the dip we hoped for.
"We were talking a month ago of getting down to 200 or so cases by the end of February… we find ourselves stuck at 500 or even higher cases per day.”
However, he stressed the country is not back at square one.
Nursing home residents and staff are now almost completely vaccinated, while the vaccination programme is ‘well into dose two’ for frontline healthcare workers.
Dr Henry said the first goal of the vaccination programme is to reduce serious illness, hospitalisations and deaths among vulnerable groups.
Then there's the aim of achieving 'herd immunity' in the population, once a large percentage of people have been vaccinated.
However, he pointed to comments from the World Health Organisation (WHO), who've said that the vaccines must be used alongside the other public health measures such as social distancing.
In terms of reopening, the HSE CCO said that will ultimately be a decision for Government.
He said: “We’ve always known that the lower we get the figures down, the more choices we have.
"At 500-600 cases per day, it considerably narrows our choices."
The Government is considering which restrictions will be eased from April 5th, with reopening construction said to be an 'absolute priority'.
Dr Henry said there is reason for 'great hope', and he believes the imminent introduction of mandatory hotel quarantine is something to be supported.
He acknowledged that there's a need to investigate the 20-30% of COVID-19 outbreaks where full tracing of the source doesn't happen.
However, he said source investigation only becomes 'very effective' when the virus is already at very low levels.
For now, he said the restrictions are needed to really drive down case numbers - then public health officials can work to prevent the virus from re-emerging.