Not only air travel. Sea travel. A thousand years ago there was an entire backup continent (the new world). And plenty of isolated communities were decimated wh

Not only air travel. Sea travel. A thousand years ago there was an entire backup continent (the new world). And plenty of isolated communities were decimated when explorers came and brought alien diseases. Air travel just accelerated the process so that pandemics can spread within days rather than years and the effects can be seen in real time.