When vampires die they became dust (kinda conventional eh? XD)

If A infect B, B is a lesser degree Vampire than A. So A > B

The process will goes on so A > B > C > D > E...turning the infected to lesser and lesser degree. All A infect is in same degree though. So if A infect B1 and B2, both have same degree.

At one point, say in H, the resulting infection will no longer vampire, but death. H is the lowermost degree of Vampires, and can't infect further. They still need to feed though. The lesser their degree, the more hunger they have. Also, they got weaker by Vampire standard (in this case, A is the strongest of all).

That's the only technical part in this plot I think. Do you find it too cumbersome?