A top immunologist is urging vaccination providers to be extremely cautious after 27 instances have occurred of incorrect dose levels being administered to adults and children.

The Ministry of Health has confirmed 27 "dose errors" have happened since January 17, the start of the Covid-19 vaccine rollout for 5 to 11-year-olds.

The errors included instances of children being administered adult doses and adults - people 12 and older - being given children's doses.

The paediatric dose administered to children is about a third of the adult dose.

National immunisation programme director Astrid Koornneef said adults who received a paediatric dose would require clinical advice as to whether an additional dose was needed to top-up their vaccination.

For children who were given an adult dose, Koornneef warned it may cause a strong reaction.

"They may unfortunately experience some stronger side effects, such as increased nausea or dizziness, but this should pass," she said.

"Parents or guardians should consult their health professional if they have any questions or concerns."

Koornneef said the vaccination provider was responsible for contacting people who were given the wrong dose to provide advice and support.

The NZ Herald has asked the Ministry of Health to specify how many of the 27 dose errors were children being given adult doses and vice versa.

Koornneef said it was expected such incidents would happen considering the scale of the rollout and the complexity of the vaccines.

The Ministry of Health and the Immunisation Advisory Centre were notified when a vaccination error occurred. Both provided clinical advice and guidance to the provider and would share any lessons learned from the incident with the wider workforce.

Immunologist Professor Graham Le Gros, director of Wellington's Malaghan Institute of Medical Research. Photo / NZME

Immunologist Professor Graham Le Gros, director of Wellington's Malaghan Institute of Medical Research, said any such errors posed serious risks.

"Everyone can make a mistake but still, given the level of concern, one is unacceptable," he said.

"I think 0 [errors] is what the public demands at the moment."

He said giving paediatric doses to adults could give them lower immunity - a dangerous scenario particularly for older Kiwis who thought they were fully vaccinated.

Le Gros also sympathised with any children who had been administered an adult dose and hoped they had been well cared for.

While he was buoyed by the notification protocol, Le Gros urged vaccination providers to be innovative in how they could reduce the likelihood of dose errors occurring.

He said administering child and adult doses on different days could be an effective strategy, as well as using separate rooms or dividing staff into groups which administered the different doses.