Right when they introduced the kurono alien storyline, which isn't a part of the manga at all.
Instead there was a mission where Kurono was by himself, and he didn't manage to kill all the aliens in the timeframe, and the result was that he lost all his points. After that, new reoccuring characters started appearing. People are actually doing a good job of surviving right now, although that might change in the current storyline...
Vampires get introduced later on, basically they can see Gantzers during and outside missions. I think that subplot is fucking stupid (Kurono's brother becomes a vampire), but whatever. Thankfully they haven't served as anything but badguy fodder so far.