> To be honest, I'm confused by the amount of air travel that is still going on. If locking down large swathes of most countries is on the cards, why is there any air travel happening?

I think essentially all the data we have indicates that there is a surprisingly low rate covid transmission on airplanes and airports. (You can be worried that the data is being provided by airline companies who are biased, but at this point I think you have to postulate a pretty big conspiracy in order to explain the consistent signal.) Assuming that's true, it means:

1. Your concern should be with any method of travel, not air travel per se.

2. Your concern should be with travel between areas with very different rates of covid (or of different variants), not travel in general. If an infected person in country A swaps places (through flight) with an infected person in country B, nothing has changed regarding covid transmission.