The Dublin Midlands Hospital group has confirmed that 572 people did not attend their vaccination appointments at Citywest yesterday.
Out of the 1,329 scheduled slots, only 757 attended.
Asked about this today, Health Service Executive CEO Paul Reid said it would not lead to the waste of any vials of vaccines as "they are opened as the day progresses and as they are needed".
The HSE, in a statement, said Citywest Vaccination Centre is in the process of completing the vaccinations of healthcare workers.
"The centre has found that the status of the registered person may change to vaccinated if contacted by another vaccination centre and this has resulted in people not attending for appointment.
"The vaccine is managed in strict accordance with the national sequencing guidance. Only the required vaccines are issued from pharmacy to meet the needs of those queuing in the centre. No vaccine was wasted."
The HSE said appointments are being made using data available on the national portal and the booking process is being managed one week in advance.
"Citywest Vaccination Centre is working closely working with the HSE National ICT team who are working on the scheduling component of the national system. This will improve the operational management of the centre and customer experience."