Cannot remember name of horror movie

I am looking for a horror movie that I just cannot remember. I saw it quite a long time ago and I only remember a particular scene.

The scene was as follows: the atmosphere is dark, with an orange-green glow. A soldier (or man with armed equipment) is shooting at a zombie horde from behind a fence, so the others can escape. Then suddenly he gets torn apart by a monster. The next thing they show is of a guy and a girl, who is partially infected, (if I recall correctly he is in love with her) hiding/escaping via an air duct. However, the girl starts turning into a zombie or infected person and the guy has to shoot her.

I also remember that the zombies/infected were able to smell the girl's blood.

If someone knows this movie or has an idea what I'm talking about, please let me know. Massive thanks.