Post apocalyptic story with very abrupt ending

Read this book a long time ago so some details could be off. General story is about the survivors trying to make it through a virus that turns people into rage zombie like monsters. I think it was theorized or implied technology was spreading the disease? The one big thing I remember about the story though is the ending >! It was a super abrupt scene in which I believe the trio are traveling down the road, and the girl in the group just gets nailed by someone throwing a brick out of their car!< I remember thinking it had to be Stephen King, google says The Stand but I don’t remember factions really playing into it. I remember it mostly being about surviving the crazed people that turned