I'm not sure if it's the case but maybe 60% is the possible maximum? I hope I understand it correctly how germs spread. Is it like this? Imagine an infected p

I'm not sure if it's the case but maybe 60% is the possible maximum? I hope I understand it correctly how germs spread. Is it like this? Imagine an infected person infects 4 other persons, and the incubation period was 1 year. Probably everyone would get the germ. But if the incubation period was 1 second, at a certain point 1 infected person would find less than 1 person who is infectable (not already infected / had an infection that is gone now / has had an immunity? / etc.).