Weeks into a zombie outbreak an elusive serial killer finds refuge with a group of survivors in an isolated country home. One of the survivors a pregnant nurse, might be a victim he left for dead years ago

My main concern with this logline is we don't know who the main character is. P.O.V is so important with loglines.

The way this reads it sounds like the Series Killer is the protag. If that is the case is his goal to kill her or hide his identity from her?

If the nurse is the protag whats her goal? to survive him and the Zombie outbreak simultanesously?

Basically figure out who the protag is going to be. From here tell us what their goal is (hopefully something more in depth than 'survive the outbreak'). This should really help tighten up the logline.

hope it helps