Anne Rice popularized the idea that a vampire should have a reflection, being that they have a physical body and we now have a more scientific understanding of mirrors. This wasn't an original notion, of course, as many ancient vampires were believed to have reflections–and mirrors were used to repel them.

Do vampires have a reflection?

Although not traditionally regarded as an apotropaic, mirrors have been used to ward off vampires when placed, facing outwards, on a door (in some cultures, vampires do not have a reflection and sometimes do not cast a shadow, perhaps as a manifestation of the vampire's lack of a soul).

How come vampires have no reflection?

[Vampires] The reason vampires cannot see their reflection is because mirrors backed with silver burn up their reflection.