New Zealand is different because it eliminated the virus.
By April the infection had been isolated and through May they basically ensured the few people who had it were kept away from everybody else long enough to recover, by June they were finished and getting back to normal. Every new reported infection in New Zealand for the last 70+ days is a person in quarantine or "managed isolation" because they arrived from somewhere it's endemic. Will it leak eventually? Probably, and they're ready for that. [Edited to remove claim that New Zealand is unique when several other countries also eliminated this virus as pointed out by another poster]
They hoped Australia could do the same, and then they'd open the border to Australia, but Australia botched it and now has a high rate of new infections.
New South Wales has elevated case levels. It's not as obviously terrible as Victoria but it's going the wrong direction.
I actually didn't know about Vietnam and Thailand, so thanks for that. But again it seems like elimination was a conscious strategy like in New Zealand. So in my opinion strategy is the difference, not some innate biological quirk shared by people across New Zealand and Vietnam but apparently not in parts of Australia.
NSW has received cases from the Victoria bungle. There's little regard for social distancing or shut down measures. We're screwed now. It's just a matter of time.
If NZ is because it eliminated the virus, then it will all happen again when (inevitably, in a virus this widespread throughout the world) someone brings it back in.
Yes, unlike prior to the pandemic New Zealand is burdened by now requiring border controls to prevent re-infection and a test & trace infrastructure to find anything that slips past and stop community transmission.
All this is of course still much cheaper than the alternative.
By April the infection had been isolated and through May they basically ensured the few people who had it were kept away from everybody else long enough to recover, by June they were finished and getting back to normal. Every new reported infection in New Zealand for the last 70+ days is a person in quarantine or "managed isolation" because they arrived from somewhere it's endemic. Will it leak eventually? Probably, and they're ready for that. [Edited to remove claim that New Zealand is unique when several other countries also eliminated this virus as pointed out by another poster]
They hoped Australia could do the same, and then they'd open the border to Australia, but Australia botched it and now has a high rate of new infections.