The Government is being warned its self-isolation trial for vaccinated Kiwis later this year could be "quite challenging" to control.
The pilot, taking place in October through December with a limited number of participants, is part of the Government's plan to slowly open up New Zealand to the rest of the world.
Prime Minister Jacinda Ardern, speaking at the Reconnecting New Zealanders to the World forum in Wellington on Thursday, said the pilot will test the ability to monitor or enforce compliance, and the management of COVID-19 cases if they arise.
"This will be available to groups of people who meet a tight set of criteria - New Zealand citizens and permanent residents who are fully vaccinated in New Zealand and have made a short trip away from New Zealand, travelling to an approved list of countries," she said.
"They will have to supply a self-quarantine plan as part of their application that meets the Ministry of Health's requirements.
"We will confirm specific details in September, including establishing an Expression of Interest process, and it is our intention to work with employers who need employees to travel for work for this pilot. The reason for this is the extra assurance that having an employer involved, with a bit of skin in the game, will provide."
But the Strategic COVID-19 Public Health Advisory Group's advice, which formed the Government's response, raised concerns about self-isolation.
"Earlier in New Zealand's response to the pandemic, returning travellers who were required to quarantine at home did not do so consistently, and measures to check on their adherence turned out to be largely ineffective," the advice says.
"Various steps could be taken to enforce self-isolation, but this option has become less attractive with the Delta variant."
The advice questions whether self-isolation could be controlled properly, given that many people live with family members. And with the more transmissible Delta variant now dominant, the risk of an outbreak is heightened.
"Experience in Sydney and elsewhere suggests that, with the more transmissible variant, other members of the household (as well as any visitors to the home) will be very likely to become infected themselves - even if efforts are made to keep apart. So there would be a significant risk of leakage of infection into the community."
The experts suggested a reduced time in a managed isolation and quarantine (MIQ) facility, from five to seven days. This could be followed by additional testing once or twice in the second week.
Ardern told reporters the pilot will be carefully managed, and that the Government took advice from Sir David Skegg, chair of the Strategic COVID-19 Public Health Advisory Group's advice.
"Five days in MIQ and the balance at home... That was part of his advice," she said. "We then tested with him a full 14-day trial of self-isolation and with the parameters that we set out with the group and the scale, the sense we got is they were comfortable with that pilot."
Ardern said it will be "vastly different" from when Kiwis were instructed to self-isolate upon return early last year, back when the COVID-19 pandemic first began and MIQ hadn't yet been established.
"There is no room for error in the first six months so we simply will not take risks that we are not absolutely convinced we can manage," she said.
"The only people who will be able to participate in this pilot will be vaccinated travellers who have been vaccinated in New Zealand and are going for short duration trips, into countries that are approved."
Sir David Skegg told reporters it will need to be tightly controlled.
"Self-isolation, as it existed before, would be not a good idea, even with that virus, let alone the Delta virus," he said. "But what the Prime Minister has made clear is that, for this pilot, it will just be people who can isolate alone."
But even with that assurance, Sir David said it won't be straightforward.
"There's two issues: one is making sure people really stay at home - we all saw those television pictures last year of people who were supposed to be isolating, tourists who were looking at the sites in Queenstown."
Another issue is food.
"Obviously we then have to have a way of getting food to them, don't we? You know, 14 days," Sir David said.
"I was one of the people who thought home isolation is a good idea, but I'm having to modify my thinking and realise it won't work for everyone.
"One of the things that worries me is, people say 'as long as somebody's vaccinated, isolation at home', and they forget that vaccination is not 100 percent effective and the kind of home isolation we had before just won't cut the mustard."
Could we follow the UK?
In the UK, people returning must either self-isolate or quarantine for 10 days, depending on where they've been.
The UK National Health Service or NHS carries out checks by phone and in person on people who have a legal duty to quarantine at home after travelling abroad.
NHS Test and Trace, a British government agency set up last year to track and help prevent the spread of COVID-19, will contact self-isolators daily to confirm they're following quarantine rules.
Rule-breakers may face a penalty of up to £10,000 (NZ$19,7000).
