Requiring an invitation to enter a place is but one similarity between the villains in Carmilla (1872) and the Gothic poem Christabel (from the late 18th c.); in the latter, the evil stranger Geraldine cannot cross the threshold to Christabel's family home on her own:
The lady sank, belike through pain,
And Christabel with might and main
Lifted her up, a weary weight,
Over the threshold of the gate:
Then the lady rose again,
And moved, as she were not in pain.
Stoker's Count (1897) needed an invitation to enter a house (was he taking a cue from leFanu?), as did the vampires in Salem's Lot (1975).