Vampires are regular people who ingest mage blood for the magical properties, namely strength, endurance, and agility. The potency of the effect is proportional to the strength of the mage. The most common vampires in the 1800s were archers and thieves as the agility enhancements were vastly more pronounced than the others.
Little scientific research was done into vampirism, but one notable enhancement was when a mage created a potion using their own blood. This potion could infuse vampires with elemental properties. This breakthrough lead to the Mage Council criminalizing the act of mages freely giving blood to regulars. These events lead to the War of Blood between mages and vampires in 1850.
By the time the Mage Council created New London in 1854, those who practiced vampirism had been hunted to extinction. It re-emerged in the 1960s when unemployed mages left New London looking for work. Vamp bars opened, owned by low-level mages whose blood wasn’t powerful enough to create traditional vampires, but strong enough to create a nice high.