Of course some countries have dramatically different demographics, geography and medical systems than others which can have a huge effect. As has been pointed out in a parallel thread Vietnam locked down all international travel very early, and demographically has a far younger population than most nations which has a huge effect on relative mortality rates.
For New Zealand they have an extremely widely geographically dispersed population, which you can think of as built-in demographic social distancing. They also locked down early and there was strong popular support for the lockdown.
It's really pretty ridiculous to expect radically different countries with completely different geography, demographics, medical systems and lockdown policies as though they're all assumed to be equivalent as a default. Specific local conditions can have a massive effect. But anyway I'm not even sure I understand what your point is Why do you think these countries outcomes were so radically different from, say, that in New York, or Lombardy? Or what's happening right now in Texas?
> For New Zealand they have an extremely widely geographically dispersed population
I don't know the answer, but is this actually true? Sure, the density as measured as a ratio between population and land mass indicates a dispersed population, but is the population not centered in a handful of cities?
A quick search indicates that Auckland, a single city, contains a third of New Zealand's population.
FWIW Vietnam's youthful demographics are pretty much irrelevant; what's impressive about Vietnam is not its mortality rate but that they shut down viral transmission.
My point is that many countries with wildly different conditions have successfully suppressed the virus, which I think suggests that just about any country could have suppressed the virus with the right policies. At least, one should not confidently assert that there is no way the USA, western Europe, etc could have successfully suppressed the virus.
> FWIW Vietnam's youthful demographics are pretty much irrelevant; what's impressive about Vietnam is not its mortality rate but that they shut down viral transmission
The young are less likely to get sick, those who don't get sick are less likely to spread the virus. Youthful demographics are not irrelevant to shutting down viral transmission.
I have had the impression that the age effect on sickness and transmission is much less than on mortality, but I admit I don't remember any specific data on that.
I'm not saying they couldn't have suppressed it, I'm saying they couldn't have done so without a lockdown. Once the virus is progressing through your population there's no other way, though masks certainly seem to help. With sufficient testing you can track it's progress and employ smarter lockdown strategies of course.
As to your final question(s): I think the key differences are: developing a national strategy to defeat the virus, not live with it; clearly communicating that strategy; and sticking to it.
Countries with SARS experience were quick at developing and communicating those strategies. Other countries like NZ and Australia were not absolutely quick but were quick enough because the virus got here later.
For New Zealand they have an extremely widely geographically dispersed population, which you can think of as built-in demographic social distancing. They also locked down early and there was strong popular support for the lockdown.
It's really pretty ridiculous to expect radically different countries with completely different geography, demographics, medical systems and lockdown policies as though they're all assumed to be equivalent as a default. Specific local conditions can have a massive effect. But anyway I'm not even sure I understand what your point is Why do you think these countries outcomes were so radically different from, say, that in New York, or Lombardy? Or what's happening right now in Texas?