Prime Minister Jacinda Ardern says if Kiwis had the choice between "less friction" at the border or a lowered risk of having to go into lockdown, they'd likely opt for the latter.
Her comments come as experts say the risk posed by the Delta variant will wipe out much of the gains made by the vaccine rollout, since Kiwis aren't using the COVID Tracer app enough.
Delta was discovered in India late last year, and is significantly more infectious than the original strain of SARS-CoV-2 - the virus which causes COVID-19 - that emerged from China. There is growing evidence that while the existing vaccines are still good at preventing serious illness and death from Delta, they don't do much to stop transmission.
University of Auckland disease modeller Shaun Hendy told Stuff the risk of a hard level 4 lockdown now is about the same as it was last year, despite about 16 percent of Kiwis being fully vaccinated.
Fewer than 300,000 Kiwis are using the COVID Tracer app each day, meaning contact tracers will have a tough time tracking down people who might have been exposed to the virus, should there be a case in the community here. If people potentially carrying the virus can't be traced, then a level 4 lockdown will be required, Dr Hendy says.
Scans have nearly halved since June, when New South Wales' stubborn outbreak of Delta began. The state's leaders have resisted a full lockdown, allowing the virus to get a foothold in Sydney that continues to grow.
University of Otago epidemiologist Michael Baker said an "intense lockdown, as fast as possible" here - like we did in March last year - might work, but it may also require mask mandates in places like gyms, bars and nightclubs, which have been shown overseas to be transmission hotspots.
Ardern, also speaking to Stuff, said with most Kiwis still unvaccinated our options in the case of an outbreak are limited - a lockdown would be needed. She said widespread vaccination would reduce the risk of needing to go into lockdown, but wouldn't put a number on how many Kiwis would need to be vaccinated before the border would open.
Australia has put its figure at 80 percent of the present eligible population, which excludes children under 12 - so about 64 percent in reality, which some experts have said is nowhere near herd immunity, and places children at risk.
"I ask people: If you had a choice what would you want to get rid of first, the uncertainty of a really heavy level 3 or level 4 lockdown, versus a bit less friction at the border?" Ardern told Stuff.
“People want to get rid of the idea that at any moment in time a big life event might end up being cancelled because you're going into a lockdown. That hangs over people."
New Zealand hasn't had a case leak through the border in more than five months. Ardern says this has allowed Kiwis to live life without restrictions on movement or social gatherings, and let the economy flourish - saying this week's unemployment figures of 4 percent would have been something to celebrate in normal times, let alone in the midst of a pandemic.