The online portal for children aged between 12 and 15 to register for their coronavirus vaccine opened earlier than expected on Wednesday night.
It was due to open for this group tomorrow, but instead it appeared to launch ahead of schedule tonight.
Kids availing of the jab will receive their vaccine "within days" of registering, according to the HSE.
The majority of these young people will be inoculated in vaccination centres, with some others likely to get the injection from GPs or pharmacies.
Damien McCallion, the HSE's national lead for the Covid-19 vaccination programme, said it will be just "a couple of days" before the vaccines to young teens will begin being administered.
For the 12-15-year-old group, parental consent will be required before they can receive their vaccines, which will be either Pfizer or Moderna.
Mr McCallion said that as many slots as possible will be allocated to parents who register their children on Thursday, Friday and into the weekend.
He added that he was conscious that parents and guardians will have concerns about vaccinating children and advised them to access all information available from the health service and experts before making up their minds.
He expects that everyone in Ireland over the age of 12 will be vaccinated by mid-September, with the HSE pinpointing the end of August for when nearly all adults will be inoculated.
It comes as a 'late night' vaccination centre for people who are unable to visit the clinics during working hours will open on Thursday.
Citywest Vaccination Centre in Dublin will operate walk-in Dose 1 Covid-19 vaccination clinics again this Thursday, August 12 for a late night clinic from 6pm to 10pm.
This clinic will be open to anyone in Ireland over the age of 16 who is not yet vaccinated. They can attend this walk-in clinic and get a first dose of a vaccine.
Phil O’Neill, Chief Operations Officer at the Citywest Vaccination Centre: “So far the walk-in clinics have been a resounding success. To see the great numbers of young people that have turned up to get their vaccine is truly inspirational.
"The turnout at the walk-in clinics has been predominantly younger cohorts but there was a representation from all age groups.
"For that reason we are opening up the Citywest Vaccination Centre for a late night walk-in clinic on Thursday 12th August. We feel that this might particularly appeal to people who may not have been able to make appointments offered previously due to work or childcare commitments.
"We would encourage anyone who hasn’t yet received their vaccine to come along.”
