They periodically reimport it.

If I had to guess, I would guess that COVID can be transmitted by fomites, especially if kept cold, but that it’s extremely rare. In a place like the US or Europe, this is insignificant: your chance of getting seriously sick due to touching something is negligible, and the rate of additional cases due to this effect is inconsequential for public health. But in AU or NZ, where the background rate is essentially zero, a single reintroduction is a big deal.

Although I largely agree with you, they found a case in Norway where the most likely explanation was contact spreading from a person who had worked in that area 2 days prior. I feel there must be another explanation, but they do probably know the facts a lot better than me.

> They periodically reimport it.

Right, so why would the US - with much more porous borders - somehow do better?

I think doing as well as NZ would be a laudable goal. If the whole world did that well, then I think COVID would be quickly eradicated.

But, beyond the fact that the US has large land borders, the US has a genuine problem. We are economically dependent on legal and illegal cross-border seasonal migration. I personally think that, with actual political will, the borders could be made a lot less porous, but this would involve attacking the supply and demand sides. Neither party is interested.