shlucha > they had weak immune system, even a simple sneeze caused them to die.
sounds plausibly. don’t you see it now? if you have a weak immune system (or just towards particular patogen), then you get seriously sick and soon after someone sneezes (nose is irritated), the lungs will be affected too.
and weak immune system (comparing to now) may be due to lower travel and community mixing, and also probably less crumbing people in the same room. Urban life changed a lot. For example, 19th century brought sickness from spoiled milk that was transported from villages to cities until pasteurization was instituted (which was protested by non-believers and as much as vaccines now).