A question on Vampire bites ...

Does anyone know how to tell if a Vampire bite will result in turning the bitten Sim into a Vampire if the bite was from a non-controlled Vampire.  I ask because one of my Sims was bitten while she was sleeping by a random Vampire, but nothing happened except she fell asleep (fainted) and then felt uncomfortable all day.  I thought this was because the Vampire who bit her wasn't powerful enough to turn her into a Vampire, but then a few nights later Vlad came over and did the same thing.  I was sure my Sim would change into a Vampire, since Vlad is so powerful, but the same thing happened as it did with the lesser Vampire!  😮🤔  Thanks!