Okay, but it still remains that not all exposure to infectious things always gets you sick (though it is, of course, a risky gamble). And that's not even taking into account the theory that Tuuri might be actually immune. It's a comic that contains magic after all, you can't draw conclusions like you would in real life, especially since the illness seems to be at least partly magic in nature.
Also @ rifle size, I don't know if you've noticed but the author is not anywhere near into weapons. Not saying this to put her down, but she doesn't even research the correct size and firing position for guns, why do you expect her to know or take into account what impact a certain caliber weapon would have at a certain distance? You probably know these things naturally if you work with guns often, but the rest of us have to research it carefully if we're to get it right, and sometimes it's hard to know WHAT to research.