I think NZ closed their borders with harsh restrictions and therefore did quite well at keeping it out.
Isle of Man did similar. It was pretty normal in IOM, but then when covid found it's way in (via a ferry worker), there were hundreds of cases in a very short time frame, which needed another harsh lockdown to control.
Luckily, both IOM and NZ could do harsh border controls. Unlike mainland UK, they didn't have thousands of cars/vans/lorries in and out of their borders every day delivering essentials. IOM and NZ imports/exports were more "container" based so containers could be left at ports meaning drivers weren't going with their goods. We couldn't do that in the UK.