A computer glitch meant the HSE’s Covid vaccination portal left the data of up to one million people vulnerable.
This included the full names, vaccination status and type of vaccination people received.
The issue was discovered in December 2021 by Aaron Costello, security researcher and principal software-as-a-service security engineer at cybersecurity company AppOmni.
There has been no indication yet that the information was accessed by any users with malicious intent.
The HSE confirmed the problem had arisen, pointing to the “time pressure” the Covid-19 vaccination campaign was under.
The breach came just months after over 100,000 patients had their personal data hacked in a major breach of the health service’s computer systems.
It said the problem had been remedied the day it was alerted to it.
“If someone accessed data, we would be able to see this in the detailed logs which we analysed,” the HSE said in a statement.
Speaking on the root cause of the leak, Mr Costello said: "The vaccination portal, built on top of Salesforce, allowed any individual to sign up to the portal through a self-registration form. In Salesforce nomenclature, this particular type of portal is known as a Lightning Community or Digital Community.
"Unfortunately, the individuals who had configured the profile’s permissions had accidentally granted the profile an unprecedented level of access to the Health Cloud object that is responsible for storing information specifically about vaccination administration.
"Thankfully, the ability to see everyone’s vaccination administration details was not immediately obvious to regular users who were using the portal as intended."
