This is about to sound crazy. Okay, so when I was younger I use to watch a lot of low budget horror films on the channel called Chiller. I remember watching a movie about religious people going crazy and killing other people and they said it would save yourself if you killed your self and everyone around you. It was kind of like a pandemic. It also had a group of survivors who were being chased and they had one of the crazy religious people in their captivity. I can’t remember who was in it or who directed it. All I remember is that they had cross shaped daggers they would use to kill everyone else.
The End of the Line (2009)?
https://www.imdb.com/title/tt1176727/
Believers (2007)
https://www.imdb.com/title/tt0878652/
I think this is probably the film GG meant to suggest:
End of the Line (2007)
https://www.imdb.com/title/tt0494224/
The Visitation (2006)