The 95%+ vaccinations rates (12+) in the three major cities and 92% overall (also 12+) would somewhat help. Along with the fact community spread is already present and has been for a few months, the measures in place have kept uncontrolled spread in check.
NZ keeps new introductions to a minimum to ensure that contact tracing is not overwhelmed and this adds to the effective decrease in reproduction offered by vaccinations. New Zealand being a season behind also allows the Northern hemisphere to burn through a wave and NZ can then decide when to lift international arrival restrictions to a time when the incidence levels are low from common arrival locales (UK, US etc).
NZ keeps new introductions to a minimum to ensure that contact tracing is not overwhelmed and this adds to the effective decrease in reproduction offered by vaccinations. New Zealand being a season behind also allows the Northern hemisphere to burn through a wave and NZ can then decide when to lift international arrival restrictions to a time when the incidence levels are low from common arrival locales (UK, US etc).