A quarter of New Zealand may end up unvaccinated against Covid-19 but experts say that might not be a big problem if the country's most vulnerable are protected.
Having a large percentage of the population unvaccinated threatens New Zealand's ability to reach "herd immunity", which is when enough people have immunity, either from vaccination or a past infection, to stop uncontrolled spread.
Herd immunity doesn't make any one person immune, and outbreaks can still occur. It means that a virus is no longer easily jumping from person to person, helping to protect those who are still vulnerable to catching it.
Nobody knows for sure what the herd immunity threshold is for Covid, though many experts say it's 70 per cent or higher.
However, Immunisation Advisory Centre medical director Peter McIntyre says even with New Zealand children and those who refuse a vaccine unvaccinated, it wouldn't completely jeopardise the country's return to open borders.
When New Zealand begins its vaccine rollout to the entire population, set for July, people aged 16 and over will be offered a vaccine, leaving roughly 1 million Kiwis under 16 years old unvaccinated.
Last week, director general of health Dr Ashley Bloomfield said people aged between 12 and 15 years old - approximately 250,000 people - may also be included in the national rollout if Medsafe approval, expected by the end of the month, was granted.
This would mean about 15 per cent of the population wouldn't be offered a vaccine.
A survey of 1400 respondents between September and March, conducted by Horizon Research, indicated about 10 per cent would "definitely not" get a vaccine, and one in five respondents were unlikely to take a vaccine.
Together, about 25 per cent of Kiwis wouldn't be vaccinated by the time the national rollout, as it stands, ended.
Although that may appear a problem, McIntyre said it was important to recognise the relative risk to different populations.
He explained that early evidence indicated young children were not as susceptible to the virus and didn't easily pass it on - which meant they may not need vaccinating.
"If we get a really high percentage of those vulnerable people vaccinated, then that might be enough to get Covid into a situation where we can handle it," he said.
"We could be down to a situation where, sure there are still some cases and some will be severe and some people might die, but compared to what it's like with influenza in the past, it'll be pretty good."
McIntyre was quick to point out the overall benefits of having more people vaccinated than unvaccinated, as some areas of New Zealand would have lower vaccination rates than others and that the vaccine was only about 90 per cent effective.
"The highest priority should be to get to 100 per cent of vulnerable people [vaccinated]."
University of Otago epidemiologist Michael Baker said there were two schools of thought regarding how New Zealand might manage the virus in the long-term.
One was "endemic infection", which circulates in the community with those vulnerable getting vaccinated. About 500 Kiwis die annually from influenza.
The other was "long-term elimination", where - similar to measles - concerted efforts are made to achieve high vaccination coverage and stop the disease circulating.
Baker said although evidence on Covid-19's impact on children was in its early days, he would lean towards a long-term elimination approach as it gave further protection at a wider level.
Asked why that approach was not taken with influenza, Baker said a key aspect was the efficacy of the vaccine, which was about 70 per cent. If New Zealand had a more effective vaccine, Baker believed elimination would be attempted.
He saw a crucial factor in any future Covid management plan would be analysing the virus' ability to spread through vaccinated communities, something which would become clearer as countries reached the end of their vaccine rollouts.