A further 783 cases of Covid-19 have been confirmed in the Republic on Wednesday.
It is the largest number of new cases in almost five months, representing the highest daily figure reported since February 20th.
In an update on the national coronavirus situation, the National Public Health Emergency Team (Nphet) said the country is now in the early stages of exponential growth with the Delta variant.
Numbers are currently tracking the "pessimistic" scenario previously forecast by Nphet, the group said, and case counts will double every 15 to 30 days if nothing else changes.
In modelling from Nphet at the end of June, this "pessimistic" scenario predicted 681,900 new cases by the end of September, with 12,985 hospital admissions, 1,685 intensive care admissions and 2,170 deaths.
Speaking this afternoon, deputy chief medical officer Dr Ronan Glynn said the situation was deteriorating across Europe, with an overall 20 per cent increase week-on-week in cases.
Dr Glynn highlighted the impact of travel on case numbers in the Republic over the past fortnight, with 626 travel-related infections identified.
He said travel now represents more than one in ten cases where contact tracers have been able to identify the likely source of disease transmission, highlighting travel from Spain, Britain and Portugal as particular sources of transmission.
Meanwhile, chair of Nphet's modelling group Professor Philip Nolan said new modelling of future growth of the disease was a "cause for considerable concern".
Current case numbers are tracking ahead of the "optimistic" scenario presented by Nphet prior to the decision to delay the reopening of indoor dining, Prof Nolan said, with the Delta variant spreading even more quickly at that time than thought.
Prof Nolan said the variant reached 70 per cent prevalence in the Republic around July 2nd or 3rd, some weeks in advance of what Nphet had predicted.
After rerunning the models and introducing the Delta variant earlier, Prof Nolan said current case counts were still tracking at the upper confidence bounds of the original "optimistic" scenario.
The country is currently tracking the "pessimistic" scenario forecast by Nphet, he added, but said that did not have to remain the case.
Case counts to double
Prof Nolan said he was optimistic that if people were presented with these facts, the public would modify their behaviour and change the trajectory of the disease as they had done before.
"We are now in the early stages of exponential growth with Delta," he said, with the current coronavirus growth rate estimated at 3.5 per cent per day.
If nothing else changes, Prof Nolan said, case counts will double every 15 to 30 days.
There remains "very significant" uncertainty about the direction the disease might take over the next six to eight weeks, he said. The bottom line was the need for caution over the next number of weeks, until a substantial majority of the adult population was fully vaccinated.
Prof Nolan particularly urged caution from younger people who are unvaccinated, adding that vaccination is now not more than a few weeks away for them.
The incidence of Covid-19 is also beginning to rise slowly in both partially and fully vaccinated cohorts, as it spills out from those aged 19 to 34, Prof Nolan said.
The R number of the disease is currently estimated to be between 1.1 and 1.3, he said.
There has been a new uptick in the number of admissions to intensive care, with at least half of current patients admitted over the last 10 days.
The latest figures show 73 people hospitalised with the disease, with 20 in intensive care.
Dr Glynn also said GPs have identified a changing symptom profile associated with the Delta variant. The new variant is presenting for many in the form of a sore throat, nasal symptoms such as a runny or blocked nose, and a headache.
Dr Glynn urged anyone experiencing such symptoms not to assume it was a cold or hayfever, but to immediately isolate and seek a test.
Meanwhile in Northern Ireland, a further 636 cases were reported on Wednesday, along with one further coronavirus-linked death. There were 72 Covid-19 positive patients in hospital in the region as of this morning, with two in intensive care.