I just read the smallpox wasn't super contagious, and some people were talking about ultra-lethal bioweapons variant of smallpox, which I thought might kill people faster than it infected. Both diseases have incubation periods where the diseases don't spread until they begin manifesting symptoms. And I knew Ebola was not really contagious, but I wasn't sure where it was on the totem poll in relation to smallpox.
The hospital also had a design that encouraged air currents, and people were exposed for much longer than most flights, not to mention how many patients were already weakened. International flights filter the air heavily; though regional flights don't. I'd think you'd have to be in the general vicinity to get infected.