Nphet has warned that while infection levels have been significantly reduced in recent weeks the situation remains "very fragile".
In a letter to the Minister of Health, the Deputy Chief Medical Officer warned that there remains a considerable risk that Ireland will experience a further wave of infection if public health restrictions were to be eased before the vaccine rollout has been significantly advanced.
Dr Ronan Glynn also warned, in his latest letter dated February 18, that hospital and ICU occupancy levels remain high.
As hospital and ICU figures fall at a slower rate than infections, Dr Glynn said there would be prolonged pressure on the acute hospital system over the coming weeks.
According to the letter, published by the Department of Health today, the majority of those hospitalised (47%) and in ICU (69%) are under the age of 70.
"As such, it can be anticipated that vaccination will not have as significant an impact of hospitalisations initially as it will on mortality as it will take time for younger age cohorts to be vaccinated."
Dr Glynn warned of the fragility of the health service and the impact on health care workers citing fatigue and burn-out as major concerns.
He added that the serious and extensive disruption to non-Covid services across the breadth of the health and social care system will be felt for some time to come.
Nphet models predict that case numbers will decline more slowly in February and March than if the R rate had been kept between 0.5 and 0.7.
"We now estimate, if R is maintained between 0.7 and 0.9, which is in itself challenging, that we will have 400-500 cases per day at the end of February and 200-350 cases per day in the week beginning March 15."
In a letter just one week previous, models suggested case numbers could be down to 100-300 by March 15.
Hospital numbers are also expected to remain high with 500-600 predicted to be hospitalised at the end of February and 80-100 requiring critical care.
Optimistic projections will see these further decrease to 300-400 in hospital and 50-70 in ICU during the third week in March. This prediction is contingent on the R number staying between 0.7-0.9.
While the rollout of vaccines is cause for some hope, Dr Glynn warned it is not possible at the moment to know what level of protection the vaccination will give.
"While we have just cause to be hopeful that things will improve over the course of the year, it is simply too early to predict what the future trajectory of the disease will be given all the uncertainties and unknowns in relation to variants and vaccine effectiveness and uptake levels."
Dr Glynn added: "It is vital that as a population we don't drop our guard and we ensure that our overall approach continues to be one that is cautious and sustainable over the immediate, medium and longer terms."
The letter pointed to recent data which shows the public's mobility is increasing although levels still remain low.
Data also shows that the average number of close contacts per adult is slowly increasing though it remains very low.
Incidence of the virus was noted to be decreasing across all adult age groups except those aged 24 and younger.
"Of note, there has been an increase in incidence in those aged 19-24 which may be due to increased social mixing in young adults."
The number of cases in Dublin was also identified as increasing although they remain lower than in earlier phases of the pandemic.
The test positivity rate had plateaued in the week to February 17 with 17 counties recording positivity rates greater than 10%.
The Health Minister was advised by Nphet that restrictions should be extended while allowing the safe return of in-school education and childcare on a cautious and phased basis.
It was also recommended non-Covid health and social care services resume as soon as possible while remaining safe for staff and patients.
"It is essential that the return of these core public services isn't interpreted as a signal of wider reopening and that other forms of interaction or mobility are now acceptable or appropriate."
Nphet said the approach over the coming months must be one of "extreme caution" with a focus on preventing a further wave of infection later in the year.