Full Moons are traditionally associated with temporal insomnia, insanity (hence the terms lunacy and lunatic) and various “magical phenomena”.
Dr Timo Partonen carried out a study of 1400 suicides and found that people were more likely to make an attempt on their life when there was a new moon (when the moon is not visible to the naked eye). Source: Wikipedia.
As vampires can’t stand the light of day, they are sure to see a lot of these full moons!