It’s not uncommon to see ‘vampire’ and ‘vampyre’ when reading about the blood sucking creature. But, the difference between a vampire and vampyre is not always explained.
Basically, a vampire is the fictional, immortal creature from mythology, and a vampyre is a real person who believes that he/she needs to drink blood or absorb the energy of another person.
Changing the spelling of the word, merely denotes the difference between the mythological character and a real person.
You probably won’t see the ‘vampyre’ spelling in many fiction novels, as the spelling is fairly new, but when researching vampires and sanguinarians, you will see the ‘Y’ used by several groups, websites, and resources.