Why were UK airports not closed to passengers at the end of January when the WHO announced a global pandemic? In the olden days, ships carrying infected passengers were quarantined and had to fly a yellow flag!
Add to this air travel's (normally) growing contribution to greenhouse gas emissions, wouldn't 100% grounded be a better target?
By the way, at the moment, the clear, contrail-free skies in the High Peak and the views from our local hills are stunning! Not to mention the blessed silence.