This is a topic that a lot of writers of vampire fiction, including I, have addressed in different ways, inconsistency within DS itself notwithstanding. DS offered the somewhat landmark idea that vampirism was a preternatural "disease" rather than an explicitly supernatural condition. Thus, since different people have different reactions to bacterial and virile infections, based on their individual constitutions, it's conceivable they would have different reactions to the bite of a vampire. Not only that, different vampires themselves might carry different strains.
In
DREAMS OF THE DARK, for example, the bite of Thomas Rathburn, whose characteristics are somewhat different than Barnabas's, causes very severe personality conflicts in Victoria Winters (to the point that some less-enlightened soul decided it was "character corruption").
I don't think any such thing was in the minds of the DS writers back in the day, but in hindsight, one can use all kinds of such devices to rationalize.
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