The effective end of elimination in Australia's two most populous states would see transtasman quarantine-free travel in the medium-term "gone", a Covid-19 modeller says.
But experts have suggested it could still be possible for New South Wales and Victoria to vaccinate their way out of Delta's grip - and even revive their hardline strategies against the virus.
More than a month on from the closure of the transtasman bubble, it remained unclear how the two countries - increasingly on different paths - might eventually reconnect.
Professor Shaun Hendy expected Australia would be reclassified as a "medium-" or "high-risk" country if it shifted completely away from elimination, as some state leaders have now indicated.
"It depends how well they move away from it, but under those circumstances, quarantine-free travel is unlikely," he said.
"It may be that, as vaccination rates go up and we can introduce things like rapid testing at the border, it won't necessarily need to be MIQ-style quarantine - and there could be options like home quarantine, or shorter, five-day MIQ stays.
"But yes, the idea of quarantine-free travel Australia would be gone."
Hendy, of Te Pūnaha Matatini, said it was also possible New Zealand could look to special arrangements with states such as Tasmania or Queensland, provided they maintained stringent controls to keep the virus out.
"But it's going to become increasingly difficult for those states to maintain elimination status if the two most populous states are letting it rip."
Further down the track, very high vaccination rates in Australia - which had a national plan to vaccinate 70 per cent of the population over 16 - could bring infection waves under control, he said.
"Although, that is very difficult with Delta. And you certainly don't want to do it from the position they may be in now, where you've got an uncontrolled outbreak."
University of Otago epidemiologist Professor Nick Wilson said high vaccination coverage could even reopen the option of hard elimination to Australia, if it wanted that.
"If they reach high coverage and achieve some herd immunity from infection spread, it may make sense to actually try to stamp out the remaining Covid that's spreading, so the whole country can enjoy the benefits of elimination," he said.
"I don't think they've thought that through properly."
Wilson also suggested New Zealand could introduce specific travel policies for different states from early next year - such as quarantine-free travel for vaccinated and tested visitors from Tasmania, but seven days of quarantine for arrivals from New South Wales and Victoria.
But considering New Zealand's zero-tolerance stance toward opening up to places with where the virus was circulating, that looked some way off.
Victoria announced 170 active Covid-19 cases today - its highest spike in 366 days - as its premier Daniel Andrews warned numbers would only keep rising.
The outbreak meant the state's restrictions would now be linked to vaccination rates - and would stay in place until 70 per cent of the eligible population had been given their first dose.
In neighbouring New South Wales, where 1288 fresh cases and seven further deaths were recorded today, Premier Gladys Berejiklian this week reiterated her position that elimination of Delta was "impossible".
"NSW has proved successful until this point in time of getting rid of other strains of Covid but the Delta strain is a game changer and every state in Australia, sooner or later, is going to have to live with Delta."
The state had also now turned to Australia's national plan of reaching a 70 per cent full vaccination rate - which could see the reopening of NSW bars and restaurants by mid-October, and vaccinated international travellers being able to fly back into home quarantine by the year's end.
Australian Prime Minister Scott Morrison has also all but given up on a hardline elimination strategy, instead pushing his country's vaccination-centred plan as the path forward.
In an opinion piece published today, Kiwi epidemiologist Tony Blakely, now based at the University of Melbourne, said he doubted herd immunity could be achieved through vaccination alone.
"We will need further measures," said Blakely, who last month suggested it was too late for New South Wales, at least, to eliminate Delta. "Like ongoing restrictions to work in concert with vaccines."
This afternoon, Prime Minister Jacinda Ardern acknowledged that Delta was "different" - but reasserted that elimination would remain New Zealand's strategy while it was vaccinating the population.
"And then we'll continue to look at all of the evidence going forward ... we've said that for some time, but for now, it is the best strategy for us," she said.
"So, yes I see different leaders in Australia are taking different positions - but I actually think you'd see generally that their view would be keeping those cases down while you vaccinate has to be the goal, and that's certainly ours."
Ardern said she was "really heartened" by results of a new Herald-Kantar poll which found 46 per cent of respondents wanted to stick with elimination, and a further 39 per cent at least backed it until more than 70 per cent of Kiwis were fully vaccinated.