They can't be near any religious objects. Remember Dracula? He was just your average Joe until the 愛 of his life dies and when he went to a chruch, he swore to God so as a punishment, God transformed him into what he is now till he learnt his lesson. THAT'S why.
It is sad and creepy. I think there are a couple of 本 out there about vampires. Check out your local としょうかん, ライブラリ and/or book store for them and あなた get your desired infomation.
