However, officials said the attack has caused “substantial cancellations across outpatient services”.
It is expected to be a few days before the system is fully restored.
Irish Foreign Minister Simon Coveney said malware had been inserted across the HSE healthcare system network “in multiple locations”.
“It’s going to take quite some time, I understand, to clean that data, piece by piece and to try to backup and protect as much of the data as we can – so this is a very serious attack.”
On Saturday, Ireland’s health minister, Stephen Donnelly, said the impact across the country “will vary” due to the data kept by hospitals, but warned there would be “cancellations in the coming days”.