After The Change
When someone is changed into a vampire does it have any affect on their complexion, the way their body looks or the way their voice sounds?
There are some differing thoughts on this among the different vampire mythologies, but it is generally accepted in modern vampire lore that once the human-to-vampire change is completed, the new-born vampire will look like the "best-case scenario" of that person as a human being.
What I mean by this is that at whatever point a human is transformed into a vampire, their body will revert to what most people would consider its most attractive form. Their skin becomes well-toned (though considerably more pale than when they were human), their complexion becomes near-perfect, their bodies take a naturally toned and perhaps muscular shape, and any signs of aging seem to practically disappear.
In addition, diseases are eliminated, injuries restored (other than missing limbs or something like that), posture becomes perfect, and hair returns to an attractive form.
It's a little unclear if this "best case scenario" means the best that particular person has ever looked, or the best that they could have possibly looked. For example, if as an adult you never weighed less than 400 pounds, would your vampire-self go to 400 pounds, or would you be more like 150-200 pounds? My guess is that it's the latter - the most attractive possible version of yourself, but I could be wrong.
While the body takes on the appearance of a youthful adult in most cases, it does not do so in cases where the human being turned is not yet of adult age. For example, if a human were 70 years old and became transformed into a vampire, they would look about 25 years old. If a human were 7 years old, they would still look 7 years old - forever. The body doesn't suddenly grow after a transformation - it just restores itself to its best possible form.
Some may ask why this is - why do vampires become an attractive version of themselves rather than, say, looking like monsters? The answer is two-fold. First, when you make a deal with the Devil, you tend to get the works. Living eternally as an old dude with a beer belly is not nearly as tempting as living eternally as a beautiful young athlete. Secondly, it is very much in a vampire's nature to use charm and seduction as methods of enticing victims. If they were not so attractive to humans, this would be considerably more difficult to do. Just as animals adapt features over time that assist in their survival, so do mythical creatures.