Modelling shows even if New Zealand reaches a COVID-19 vaccination rate of 80 percent, there would still be 60,000 hospitalisations and 7000 deaths per year, without restrictions.
Auckland University Professor Shaun Hendy, a disease modeller, says a vaccination rate of "well over" 90 percent of over 12s or into the 5-11 age group would help to control Delta, but some restrictions would need to remain.
"The modelling tells us that for Delta, population immunity is still out of reach by vaccination alone," Prof Hendy, who advises the Government on COVID-19, said on Thursday as the Te Pūnaha Matatini data was unveiled.
The data is based on the assumption of one COVID-positive person arriving into New Zealand each day, with the borders thrown open to the world again.
With more than 90 percent of the population vaccinated, the researchers say stay-at-home orders, such as alert level 3 and 4, would no longer be required. At that rate, only "moderate" public health measures would be needed.
The modelling suggests there would be around 500 hospitalisations and 50 deaths per year with more than 90 percent of the population vaccinated.
The research shows New Zealand is on track to vaccinate upwards of 80 percent of those aged over 12 against COVID-19 with the Pfizer vaccine - the only brand currently on offer to Kiwis.
Pfizer has indicated the vaccine may soon be approved for use in children aged 5-11 years, and the Te Pūnaha Matatini researchers say that means it could be possible for New Zealand to achieve more than 90 percent coverage.
About 79 percent of the eligible population have so far either had at least one dose of the vaccine or are booked to have a dose.
The modelling paints a grim picture for New Zealand if people continue to avoid getting vaccinated, the researchers say.
"The alternative is bleak," says Dr Rachelle Binny.
"Failing to reach these high levels of vaccination would mean we will need to keep relying on lockdowns and tight border restrictions to avoid thousands of fatalities. This could cripple our healthcare system, and Māori and Pacific communities would bear the brunt of this health burden."
The modelling provides a rough guide to the benefits of high vaccination rates at the population level, but not a detailed roadmap for reopening. It show that, if we want to see an end to lockdowns, New Zealand must strive for very high vaccine coverage.
It's also essential to achieve high vaccination rates not just nationally, but also in specific communities including Māori and Pasifika populations.
"The results here demonstrate the considerable benefits of achieving high vaccination coverage in the coming months," says Prof Hendy.
"The message from the modelling is that COVID-19 is going to continue to disrupt our lives for some time yet, but that we can minimise that disruption by ensuring we all get vaccinated.
"There is no magic threshold for vaccination coverage. But the higher the coverage, the less restrictions we will need in coming years. And most importantly, we need every community to be well covered by vaccination.
"We can't afford to leave anyone behind."