My reality: Jeff made it
I realize this movie isn't suppose to be taken seriously, but the scene with Jeff at the end is over for me after he actually decides to go 'back' to the cabin. The ending for that was so predictable... and why is he yelling "I made it, i made it"! If he was so scared of infection, as he was, he would not go back to the cabin. As far as I'm concerned, Jeff walked off into the distance and survived the movie.
However, I know this is not a movie that is meant to be picked apart logically. If you did that, you would get no enjoyment out of it at all. The entire thing is suppose to be silly, I get it... but it didn't have to be so predictable.