Te Whatu Ora is contacting 12,000 New Zealanders, some of whom worked as Covid-19 vaccinators, after their personal information was found to have been released in a data leak.
Chief executive Margie Apa said the information was made available on a downloadable file which was leaked to a US blogsite.
Former Te Whatu Ora employee Barry Young was arrested in December and charged with dishonestly taking health agency data and spreading it online. He pleaded not guilty and will reappear in court on February 23.
Apa said today the process of contacting every person who was affected had begun and while 12,000 have been identified so far, the number could continue to rise.