A big jump in the daily coronavirus case numbers has been attributed to increased incidence rates in children of secondary school age.
Thursday saw the highest case count for some time, an additional 617 confirmed cases of the virus, compared to 401 the previous day.
Dr Philip Nolan of the National Public Health Emergency Team (Nphet) said the trend was likely to be "transient" and that similar trends were seen after the return of primary schools earlier in the year.
He said: "It is dominated by an increased detection in those aged 13 to 18 years of age.
"So, as a very large cohort of adolescents return to school, appropriately and understandably, with any symptoms that have been referred for tests, and that is picking up some additional cases.
"But it's not confined to that group. We're also seeing a significant increase in those aged 19 to 24, in those aged 40 to 64.
"So, whereas the bulk of the cases, or a significant fraction of the cases are in the second level school-going population, the increase in incidence is spread quite widely across the population."
He said the increased case numbers indicated an increase in social mixing and mobility "across society beginning around the 12th of April".
April 12 saw some lockdown restrictions lifted, including the full return of schools, the easing of the 5km travel limit, softer limits on outdoor gatherings and the return of construction of homes and childcare facilities.
Dr Nolan said: "We've seen this before. It's likely to be transient and we hope that it will be so.
"Now, a short period of time after secondary schools open fully, we see an increase in incidence in adolescence of second level school-going age.
"Interestingly, primary schools, of course, have also reopened in that period of time, and as yet we haven't seen a significant increase in case counts in the cohort.
"Though we might expect to see some increase in incidence in that cohort over the coming days."
Chief medical officer Dr Tony Holohan returned to the Nphet briefing on Thursday for the first time since the death of his wife, Emer, in February.
Hailing the impact of the vaccine, he said it gave him "real hope and confidence" that Nphet could be "ambitious" in its recommendations for the easing of restrictions.
Nphet has also agreed new guidelines on nursing home visits, which will be implemented on May 4.
In homes where the majority of residents are fully vaccinated, people can expect to have four visits a week with two people at each visit.
There will be no specific time limits on the visits, but Nphet recommends they be allowed for at least an hour.
Non-vaccinated people will be allowed to have visitors, though they should be made aware that they are at greater risk than they would be if they were fully vaccinated.
Ireland is still seeing "concerning" levels of transmission of coronavirus, despite the country being in a "much better place" than earlier this year, the head of the health service has said.
Paul Reid warned continued vigilance is needed in tandem with the rollout of the State's Covid-19 vaccination programme.
The HSE chief executive said more than 150,000 vaccinations will be administered next week but he would not confirm whether they will reach the Government's target of 250,000.
Mr Reid said it would all depend on the delivery of supplies of the Pfizer and Johnson & Johnson vaccines, and the decision by the National Immunisation Advisory Committee (NIAC) on the use of the Johnson & Johnson vaccine.
"It's going to be over 150,000. That's what we're targeting but I can't give specifics," he told the HSE weekly Covid-19 update briefing.
"It will hugely depend on the NIAC decision."
Mr Reid added: "It's going to be over 150,000. I can't give you a definitive number but it will be our best week yet."