Vampire

Vampire Lady
The vampire lady is a character you can encounter in The Slums, upon which you get two choices: If the player succeeds in refusing her, that will end the event and all the events associated with it.
 * 1) "I'm always up for more coin!" (triggers the vampirism events)
 * 2) "No thanks" (if your mind is not high enough, it will fail and trigger the vampirism events)

If the player fails in refusing her, or decides to take her offer, she will motion the character towards her. Afterwards, she will bite him/her, thus passing the condition - adding 3 to character's Charisma and taking 3 from his/her Physique. The character is also awarded a small amount of Wealth regardless.

If infected before week 6
The next area visited by the character will trigger a vampire event: the character will once again gain 3 Charisma and lose 3 Physique. Afterwards, the character will trash the area he's in, killing and feeding upon everyone. The area becomes unavailable for the rest of the playthrough.

It also triggers new possible character endings, dependent upon what overall ending was achieved.

If infected on week 6
The vampirism will take effect after picking your character's role. See further information on Endings.

Role - Leader (infected on week 6)
The character will hypnotize the rest of the survivors, turning them into slaves and eventually building a vampire haven on the ashes of the town.

Role - Looter (infected on week 6)
The character will have a fit of hunger whilst looting, killing and draining all the other looters, thus ironically helping the survival efforts a lot.

Other roles (infected on week 6)
The character will kill other survivors, damaging the rebuilding efforts. Triggers the other endings down below, depending on the overall town ending.

Good ending
The character is researching the mysterious disease in the palace library. Finally, he/she finds the lair of the Vampire Lady deep in the sewers...

Bad ending
The Vampire Lady finds the character she infected, turns him/her fully into a vampire slave of hers and leads him/her into the sewers.

Trivia
-Vampirism seems to have a couple of stages of development. First stage manifesting moments after infection, skin turns white and fangs become elongated slightly. The infected receives boost to charisma, while taking a hit in their physique. Second stage appears after anywhere from a day to a week of being infected. The condition worsens, and if the vampire hasn't fed he will go berserk killing everyone around him. The third stage seems to induce dormancy in the disease. Infected is for all intents and purposes human, but retains his otherworldly charisma and weak physiology. Fourth stage is awakened by the vampire that infected the dormant one in the first place. It results in mental domination and making of a vampire slave.

-Vampiric condition isn't always permament, as we can see in the Good ending. From various events, we can tell a vampire has to meet one of the conditions for it's vampirism to become permament: If said conditions aren't met, the infected person will not turn fully into a vampire.
 * 1) Vampire needs to revel in his new powers, perhaps drinking blood of their own free will, rather than going berserk due to the disease.
 * 2) Vampire needs to be compelled by it's maker, after the disease goes "dormant", losing it's will in the process.

-The event where a character previously infected tries hunting down the Vampire Lady suggests, that stake to the heart is a viable method of dispatching a bloodsucker.

-Sunlight's effect on the vampires is unknown, however full vampires are hinted to stay in the sewers.