"Following this, two paediatric Pfizer vaccine batches within the New Plymouth Vaccination Hub were wrongly extended by three months rather than 10 weeks. Subsequently, 56 children between 28 March and 6 April were administered a vaccine that was past its true expiry date across three sites.
"Once the use of expired vaccines was discovered on April 6, all sites were informed, and all stock subsequently removed from circulation. This is an isolated event restricted to TDHB and has not affected vaccinations given to those aged 12 and over."
The DHB said it had received clinical vaccination that there was no need for re-vaccination or risk of harm to 36 of the children, who received a vaccine with 48 hours of its expiry.
For the other 24 who received a dose past 48 hours, advice was dependent on their clinical circumstances and they should make an individual plan with their GP or medical provider, the DHB said.
The DHB's Medical Officer of Health Dr Catherine Jackson said " I acknowledge that this news will be distressing for parents and whānau. All families are being actively be contacted and an individualised plan made with them".
All affected whānau were being offered a free appointment with their GP or medical provider to seek further advice and make an individualised plan for the next steps for their child.
The DHB said it was contacting, apologising to and reassuring whānau of affected children.
Taranaki Covid-19 Vaccination Programme senior responsible officer Bevan Clayton-Smith said "I apologise to the whānau and tamariki involved. A review was started as soon as we found out, to understand what had happened and who was affected from this".
"The TDHB then put in measures to contact and apologise to all whānau affected. This error should not have occurred, and we are putting in a comprehensive a range of modifications within our vaccination programme to prevent future events occurring.
"The paediatric vaccine programme is extremely important to keep our children safe from the Covid-19 virus and to date more than 8000 paediatric vaccines have been administered across our region."
A review of the vaccination database revealed that no other children within the programme were affected.
The Ministry of Health and IMAC - New Zealand's expert advisors on immunisation - were informed and consulted with for clinical advice to inform the next steps.