Wairarapa DHB is investigating where Prezzy cards used to pay for a staff function came from.
The DHB last month began offering $100 gift cards to those who got their first dose of the Covid-19 vaccine.
DHB chief executive Dale Oliff said the staff function was not organised by the DHB, and that misuse of DHB incentives had not been alleged.
However, it confirmed it is investigating the origin of the cards used for the event.
The Ministry of Health said it is aware of the investigation and is confident the matter is being taken seriously.