Vampires are, of course, unable to enter a dwelling to which they have never been invited to enter. So for a time, it became common for ambulance companies to be staffed entirely by vampires; after all, only a fool would turn aside the local aid society.
This arrangement has become less tenable however as humans have become addicted to increasingly noxious chemical concoctions.
(Image by Phil Gyford. Used under Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic license)