Six people were given a low dose of vaccine against Covid-19 at a vaccination site in the Bay of Plenty last month.
No one was harmed, the Bay of Plenty District Health Board said.
The board's senior response officer Brent Gilbert de Rios said a low vaccine dose contained too much dilutant (saline) solution.
Gilbert de Rios would not name the provider that gave the low doses, but said it was "adhering to Tikanga Māori protocol" and working with those affected to address the error.
"While this process is ongoing, we will respect the privacy of those affected."