I suspect that, thirty years from now with the benefit of hindsight, we will look at air travel the way we now look at tetraethyl lead. Not just because of nCoV, but also because of disease burdens we've failed to attribute to infections, in much the same way we failed to attribute crime to lead.

Over the past century, there have been two big changes in infectious disease. The first is that we've wiped out or drastically reduced most of the diseases that cause severe, attributable death and disability. The second is that we've connected the world with high-speed transport links, so that the subtle, minor diseases can spread further.

I strongly suspect that a significant portion of unattributed and subclinical illnesses are caused by infections that counterfactually would not have happened if air travel were rare or nonexistent. I think this is very likely for autoimmune conditions, which are mostly unattributed, are known to sometimes be caused by infections, and have risen greatly over time. I think this is somewhat likely for chronic fatigue and depression, including subclinical varieties that are extremely widespread. I think this is plausible for obesity, where it is approximately #3 of my hypotheses.

Or, put another way: the "hygiene hypothesis" is the opposite of true.