CEO of the Health Service Executive Paul Reid has said the damage caused by the cyber attack and the devastating impact that it has had on the health service "cannot be overstated".
Mr Reid said contined progress was being made in repairing systems.
Speaking at the HSE's weekly Covid-19 update Mr Reid said the attack "disarmed" many clinical and medical teams, "from the basic toolset they need to treat ill patients".
"It completely wiped out over 2,000 systems, which are all having to be rebuilt."
He said many public or private organisations "would have been completely overwhelmed but for the relentless passion and commitment of the HSE healthcare teams".
Mr Reid said there is likely to be a "very long lag time in the rebuilding of services".
"It's not just about getting a decryption key. We have to rebuild systems a whole different way."
"It has left a serious trail of destruction behind which we have to clean up."
Paul Reid said he wanted to say "a sincere thank you" to the public for their patience and understanding regarding the cyber attack.
He said he wants to reassure people that they are doing everything possible to mitigate the risks, and there is an "unrelenting resolve" in the HSE to restore services in an efficient and safe manner.
"Please, stick with us", Mr Reid said.
"We know that it's hurting many people, and it's hurting us. It will take us longer than we would like... but we have to be up front and clear with everybody that it is going to take longer. We are making progress and out of this we will get at some stage."
Paul Reid said of the HSE's 5,000 servers, 96% of them have been screened and protected, which he said has to be done before they can be restored.
Mr Reid said almost 50% of the HSE’s devices have been screened and protected before restoring.
"It's a big web that needs to be fixed between servers and access points."
Mr Reid said the HSE is continuing to monitor the "dark web" for patient information and data.
"We're still at risk", Mr Reid said in relation to the possible publication of data.