November brought pandemic highs for New Zealand, with 15 deaths, and daily cases pushing beyond 200 for the first time.
Health officials reported 135 community cases on Monday, and for the eighth day in a row announced no new fatalities.
COVID-19 modeller Michael Plank told AAP the R value, or effective reproductive rate, had dropped below one for the first time in several weeks, sounding notes of cautious optimism.
"It looks like case numbers peaked some time in the last week or so. They've possibly dropped a bit faster than we expected," he said.
The chief driver is vaccination rates, with 88 per cent of Kiwis aged 12 and over fully vaccinated, and 93 per cent having had their first dose.
Those rates are even higher in Auckland, the centre of the outbreak, bringing cheer and celebration from the prime minister during a breakfast television appearance on 1News.
"Really high vaccination rates in Auckland. Astonishing and fantastic. So a huge thank you to everyone in Tamaki Makaurau," she said, using the Maori name for NZ's biggest city.
Ms Ardern said she too had been surprised by the lower case numbers.
"The modelling suggested that this would happen as a result of vaccination rates, but actually perhaps (cases are) coming away a little more sharply than necessarily may have been thought," she said.
Auckland's 107-day lockdown ended on Friday when New Zealand transitioned to a vaccine-pass system, flinging open the doors to pubs, restaurants, gyms and other businesses to fully vaccinated Kiwis.
"We're in the best possible position to make this move," Ms Ardern said.
"A large number of New Zealanders are vaccinated. We can feel confident moving forward into the new framework."
University of Otago public health professor Michael Baker called the move a "paradigm shift".
"I'd be fairly optimistic going ahead we're not going to see a large increase in cases," he said.
"We're going to see clusters of cases appearing unexpectedly around the country from now on ... we'll see cases spreading upwards, not dangerously upwards."
Dr Plank agreed, citing three factors that should also limit the spread.
"We might see a small bounce in case numbers before Christmas ... but schools are going on break, people are outside lots, and on holiday."
Public health experts hope hospitalisations will not grow, given those infected system are likely to be vaccinated.
On Monday, there were 76 Kiwis in hospital with the virus, and seven in ICU.
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