Later, it occurred to me afterwards that I should have just sent him this short excerpt from Tipping Point, about how Nick, my Patient Zero, became 'a one-man fever dispenser' ~ here, in case you would like to read, or pass on to anyone else who doesn't understand!
I must point out that my 'bat fever' (I wrote this in 2017, honest!) is 100% fatal and is airborne (for very short distances and time periods only), but the principle is roughly the same.
Nick Greenaway would not start to feel ill until the next morning, though the virus was at its most contagious in that first twenty-four hours of infection. At the gym he enjoyed a full upper body workout, whooping when he exceeded his personal best on the running machine, oblivious to the pathogens released as he puffed and sweated into the air. The owner of the gym had packed in as many machines as he could; so close together were they that the bare arms on either side of Nick were soon spotted with tiny molecules of his perspiration. On his left was a doctor who'd received the vaccination several days before; on his right, a hairdresser called Annika had not.
The next day, Annika would board a plane for her annual holiday in the sun with her girlfriends, feeling a little ill but not considering, even for a moment, that a slight summer cold should stop her enjoying her two weeks in Turkey.
FYI, an excellent list that explains all types of transmission: HERE