Xombies is a 2004 science fiction/horror novel by Walter Greatshell.
The story is narrated by Louise Pangloss, A.K.A. Lulu, a seventeen-year-old girl afflicted with Chromosomal Primary Amenorrhea. This condition gives her an appearance of a girl half her age and suspends her menstrual cycle. It's this condition that spares her from Agent X, the mysterious plague that, out of nowhere, immediately changes all menstrual-age women into "Xombies".
Victims of the plague turn bright blue, become invulnerable to conventional attacks, and develop a feral desire to suck the life out of the surviving men (and women) via a "kiss of death". The male victims, in turn, become a second generation of Xombies; not susceptible to the plague until having the air sucked out of their lungs.