It was revealed this week that vaccinations given by Queenstown provider Engage Safety between December 1 and January 28, which included several mass vaccination clinics, might not have worked because the vaccine was stored at the incorrect temperature.
The vaccines posed no health risk to those who received them, and the provider has apologised for the situation.
All vaccines are required to be stored at a certain temperature, and any issues must be reported to the Immunisation Advisory Centre (Imac).
Imac director Nikki Turner said it was notified of the problem, which was picked up by an audit, last Thursday.
The Southern District Health Board made the issue public on Monday, and said it was confident there were no issues with vaccinations given by the provider after January 28.
"There is always the risk breaches in the cold chain process and the fact that we don’t have many of these is credit to those at the provider level who are making sure that temperatures are being constantly monitored," Dr Turner said.
‘‘This is really unfortunate but on the other hand we have a very effective programme right around the country.’’
All vaccination providers are obliged to meet a Ministry of Health-set cold chain storage quality standard and must be accredited.
Accreditation is carried out at a minimum of every three years, although the SDHB attempts to check providers every two years.
The process includes an inspection by an authorised reviewer, an audit to ensure vaccination policies are up to date, and an assessment of the performance of all vaccine-storing refrigerators.
Covid-19 has meant not all audits have been able to be carried out.
In April last year, the Ministry of Health issued a note that new vaccination providers would take precedence for cold chain accreditation and existing providers should complete a self-assessment form and they could continue to operate under an extension.
Vaccination providers are advised to store the Pfizer adult Covid-19 vaccine at 2degC-8degC for a maximum of 31 days, and must log when each box is put in storage.
"Fridges used for vaccine storage must have temperature loggers and alarms to inform the provider of any temperature problems," a SDHB spokeswoman said.
"We are working through exactly what happened in this situation, and why the issue was not picked up earlier."
Dr Turner said issues like this were rare, and should be a lesson to all providers.
