The countries in the Europe are now pro-active in flattening the...

The countries in the Europe are now pro-active in flattening the curve and will continue for some time. Any outbreaks will lead to aggressive tracing and isolation. That is what it will take to continue with flattening with the curve and preventing a second wave even after when their planes start flying. They have the technology to do it and I'm pretty sure many of the citizens will be compliant. As for America they are gone case now. Japan, SK, Taiwan will be doing the same pretty soon with "curve flattening" and "outbreak mitigation" measures to allow flying to happen.
Mean while in Australia, the premiers have politically hijacked their "easy" achievement due to the hyper-inflated case/death rate models to scare the public into a full lock down to flatten the curve. In fact we pretty much squashed the curve thanks to our low population density, wide geography and urban sprawl. I'd expect NZ to open their borders sooner rather than later, if their cases continue to remain close to zero, to VIC/NSW/ACT through disciplined and effective measures to minimise the chance of outbreaks. The rest of the states will realise their economies falling over the edge for their forced border closures even with intra-state flights.