A Corrections officer at Spring Hill Prison has tested positive for Covid-19.
While the officer was fully vaccinated and the majority of staff at the facility were too, just a third of the 123 inmates in the unit concerned had received one dose, and none were fully vaccinated.
Director general of health Ashley Bloomfield confirmed the case in this afternoon's 1pm update.
He said 23 people had been in contact with the officer and were now isolating.
A total of 123 people worked with the officer in the unit, Bloomfield said.
Corrections confirmed the staff member lived in Auckland.
In an email to central region staff today, Corrections said they were made aware of the case last night.
However, the staff member was fully vaccinated and asymptomatic.
He had been tested on Sunday and had been isolating since.
"As soon as we were advised of the staff member's test on Monday night we identified and contacted 23 staff who had close contact with the staff member while he was at work.
"All have been advised to isolate. These staff will not come back to work until they have returned negative tests and been cleared by the Ministry of Health."
Two men recently released from prison who had contact with the positive case were also contacted and advised to isolate and get tested.
The unit where the man worked would now operate as a "quarantine unit".
Staff would wear enhanced PPE, including a gown and goggles.
"The unit guard room and shared spaces have been deep cleaned this morning and this will be ongoing."
Prison director Scott Walker said the staff member worked at the prison on Saturday, August 28.
"That evening they were notified that they were linked to a recent location of interest.
"They immediately self-isolated and were tested on Sunday. That test returned a positive result on Monday evening."
As of August 27, 406 staff at Spring Hill had received their first Covid-19 vaccination, with 288 staff fully vaccinated.
The total number of staff at Spring Hill is 427.
At the prison, 404 inmates had received one dose of the vaccine, and 45 were fully vaccinated. Of the 123 men in the unit of concern, 46 had received one dose and none were fully vaccinated.
Across the country, 5024 Corrections staff had received their first dose, and 4116 were now fully vaccinated. The Herald has asked for the total number of staff.
However, the vaccination numbers only included those given to staff at prisons and did not include any staff who had been vaccinated in the community by their DHB.
Among inmates, 4517 have received their first dose and 1122 were fully vaccinated. The prison population changed daily but today sat at 8198 people.
Kelvin Davis, Minister of Corrections, said the staff member did the right thing after realising they had visited a location of interest.
"Despite showing no symptoms they went and got tested and I want to thank them for their vigilance.
"All staff who had contact with the Corrections officer were immediately contacted and told to isolate and get tested, while the men in the unit have also been segregated and will be tested."
Corrections had been planning for the possibility of a case "some time and I have full confidence that their thorough plans will limit any spread of the virus within the prison".
"I expect to be kept fully informed as this situation develops, including updates on the welfare of both staff and prisoners at Springhill.
"This will be an unsettling time for many at the prison and I want to acknowledge the frontline staff going to work every day while we try to eradicate the virus."
National's Corrections spokesman Simeon Brown said Corrections staff generally had a high vaccination rate.
The virus was seeping into many large workplaces in and around Auckland, he noted.