Fifteen people in Wellington have received expired Covid-19 vaccines and six people in the Bay of Plenty have received low doses.
The incidents have been reported by Covid-19 Vaccination and Immunisation Programme national director Jo Gibbs, and no-one has been harmed by receiving the expired doses, which were given 24 hours after the vaccine had expired.
In a statement, the Ministry of Health (MOH) said Capital & Coast District Health Board had contacted the affected people and was encouraging them to get vaccinated again.
"The ministry apologises for what has happened and reassures the public that such incidents are not common," it said.
"The CCDHB ... is working directly with the Immunisation Advisory Centre (IMAC) and those affected."
Those in the Bay of Plenty who were given low doses have been contacted and offered vaccination, the MOH said.
The clinical processes and systems around the administration of the vaccination are being reviewed and the District Health Board (DHB) is working with the provider to strengthen these to prevent an incident like this from happening again, it said.
Director-General of Health Dr Ashley Bloomfield said the mistakes affected only a very small percentage of people and did not expect them to erode confidence in the vaccine rollout.
"The programme has delivered over 3.6 million vaccinations and the assurance I can provide people is that that fact that these [mistakes] were found is a reflection of the quality assurance processes that are in place to make sure if there is anything that could go wrong in the context of tens of thousands of vaccinations being delivered each day, that actually out systems are here to find them and follow-up immediately."