Zombie/virus outbreak movie?

virus outbreak movie where the survivors try and get to the helicopter but the pilot gets bit so they head to a boat. There's one guy that injects himself with medicine to keep from turning into a zombie but decides to stay behind to fight zombies after his medicine ran out. Also some guy who got out of prison came back to find his girlfriend but at the end of the movie he stays behind along with the other guy so that his girlfriend could escape on the boat. The 2 guys fight zombies and at the very end of the movie the first guy starts up a chain saw while he is recording himself on video.