Health Minister Stephen Donnelly has thanked Dr Ronan Glynn for his work ahead of the return of Dr Tony Holohan tomorrow.
The acting Chief Medical Officer will return to his role as Deputy on Monday when Dr Holohan makes his return.
Dr Glynn has been in charge for one of the toughest periods of the pandemic here in Ireland and has been praised by the Fianna Fail Minister.
Minister Donnelly tweeted: "I'd like to express my sincere thanks to Ronan Glynn for all his work as Acting CMO since early July.
"He stepped into one of the toughest roles in Ireland and did a fantastic job. Looking forward to on-going work with Dr. Glynn and again now with Tony Holohan on his return.
"There have been many early mornings and late nights in the office as tough decisions were made and Ronan has an absolute pleasure to work with throughout.
"It will be of huge benefit to us all to have the expertise of Dr Holohan and Dr Glynn as we face into the challenging winter months.
"I look forward to working with them both. As always, our aim is to save lives, keep people healthy and protect our health service."
Dr Holohan will return to office on Monday and will again brief the public at meetings and liaise with Government officials.
