The European Medicines Agency said it has confidence in the safety and efficacy of mRNA Covid-19 vaccines for use among those aged 12 to 15.
It comes after the Government announced earlier this week that the Covid-19 vaccination programme will be extended to children in that age cohort.
EMA Executive Director Emer Cooke said the "impressive" performance of both the Moderna and Pfizer vaccines in older populations, at over 90%, has been replicated in children's trials.
Speaking on RTÉ's News at One, she said in authorising the vaccines for use in these younger cohorts it reviewed the trial results among "a very robust database" of 4,000 children.
The EMA is also monitoring "very carefully the experience" in both the United States and Israel, where they have vaccinated these age groups.
She said the agency investigated if any differences that might be expected as a result of children's less mature metabolism occurred and found there were not.
Ms Cooke said the rare side effect of inflammation of the heart, or myocarditis, had a slightly greater incidence as trials moved down the age groups but are still very rare at one in 20,000.
"Of course with any inflammation of the heart you have to be careful, but mostly it resolves quickly with normal therapies," she added.
Ms Cooke said the EMA will continue to watch carefully for any long-term effects of vaccines, and will have a two-year follow-up of every subject in the clinical trials.
Data on vaccine use in the under-12s has not yet been provided but studies are ongoing, she said.
The EMA said it expects to start receiving and evaluating data in the autumn for mRNA vaccines in 5 to 11 year olds.
Ms Cooke said that the EMA wants to be prepared for any new or emerging variants and so has been working with pharmaceutical companies since April on the compositions of adapted vaccines if needed.
The companies will work on the trials for adapted vaccines, she said, and when the data is ready it will be provided to the EMA for review, which can happen quickly.
There are five other vaccines under "rolling review", she added, but none have progressed as quickly as the first four for various reasons.
The Novavax vaccine has reported scale-up issues and while it has shown "very promising results" it could not assure the EMA that it could manufacture to the quality expected at scale.
Meanwhile, the Irish Secondary Students Union (ISSU) has called on all students to take up the offer of a vaccine as soon as it becomes available to them.
The vaccine registration portal has been open for 16- and 17-years old's since Tuesday.
Speaking on RTÉ's Drivetime, ISSU President Emer Neville said: "it is important for the safe return to school for as many students and teachers as possible to be vaccinated."
She said this will "safeguard the education system and let students return to some bit of normality."