Being an island might make it easier to close borders, but the point is that closing them was likely hugely significant. I'd argue that borders remained open in many countries areas largely due to a lack of will. You could certainly close borders to most tourists and business travelers in any country that does immigration control, like Australia did. You can also close interstate land borders, like Australia did. You can even close borders to major cities, like Australia did. You don't need to close borders to food deliveries, just budget for the logistical headaches. You do have to pay the political and economic cost though. Australia was watching with both envy and horror when we started seeing stories of British people able to go on holidays to Europe again.