Do vampires exist?
Do I believe that there are people who believe that vampires exist? Absolutely.
Do I believe that there are creatures who pass for human who sink fangs into the necks of others and actually draw blood? Not so much (but there are more things in heaven and earth, Horatio...)
Do I believe that there are people out of whose company you go, feeling drained and sucked dry? Oh, yes. Abso-absolutely!