Well from all the research I have done I would say that you would either have to exchange blood with a vampire by cutting a slit (not deep, enough for blood to come out) on each of your fingers. Make sure the vampire has her/his fingers cut too. And press your hands with the vampires for about five minutes to exchange the blood. Or like a lot of stories say, the vampire must bite you.
The above might be true if vampires exist, which they don't. Modern historians trace the legends of vampires to the medieval lack of understanding about the transmission of disease, combined with superstition regarding how corpses decompose.