I was at Madrid airport in June 2019 and waiting in the long line for border control to leave there was a man who was displaying extreme flu-like symptoms. Coughing, sweating, pale as a ghost. Mind you, this is the height of summer. Even back then, prior to the pandemic, I actively avoided him because he looked really unwell.

I know there is no way of knowing and at best it is a fanciful mental exercise, but I think to myself 'what if'?