How does a vampire become one?

Answer 1

Depends on the mythos to which you ascribe. Most usual form of infection is given as being bitten by a vampire but not killed or having your body obliterated. There is then a short latency period, after which you fully become a vampire.

An alternate version, more classic in nature, was that you had to trade blood by choice with a vampire. If bitten you would die, unless you bit them back. If this two way transaction occured, then you would turn into a vampire. It involves far more of a sense of choosing vampirism, as opposed to the typical forced conversion ideal of the bite = vampire mythos above.