Zombie outbreak / plague film?

I'm not positive it was a zombie plague, but some kind of plague. I remember a small group of people holding up an suv on a desolate highway. A young girl in the car is sick and they put up a cellophane barrier inside the car. They go to some form of makeshift hospital where there are no survivors. I thought it had some to do with zombies, but maybe not. (No zombies actually in it, just the sickness.)