Explanation: Most of the classic vampire lore holds that vampires are immune to diseases in general, and don't die of old age. This indicates that the cells undergo a 'perfect' replication process when damaged whether that process has ties to demonic or spiritual essences or the vampiric infection itself. There appears to be no breakdown of the genetic coding even when exposed to things which would alter it, such as radiation.
Anne Rice's vampire lore you are correct about, in that if Akasha had been destroyed, it would have potentially killed every other existing vampire as she was the original source, until she was consumed by Maharet's sister (I forget the name of her). This is a spiritual explanation for the vampiric condition which can make a certain amount of
sense but seems a bit unlikely for a few reasons:
1) If the vampiric condition is brought about by the presence of an outside spirit or essence, and the dilution of said essence directly determines the strength of a vampire it stands to reason that there is only a finite amount of this essence which can be spread and that 'creating' new vampires would drain the creator vampire of strength thus permanently weakening it in the state of creating the new vampire(s). This has not been demonstrated to be true.
2) If it is actually a conscious spiritual entity responsible for vampirism, let's say a demon, it stands to reason that at least on some level the presence of the same spirit across many creatures *should* create certain links between vampires. If it is in fact a form of demonic possession, it is not in this demon's interest to have it's vessels killing each other as vampires have done in many lores. 'Diablerie' is one term for vampires consuming the blood of other vampires to gain strength, and is often punished among vampire cultures...but more for the reason of maintaining order rather than a demonic presence attempting to keep control over it's vessels, I suspect. Much akin to our laws about murder. Other possibilities should include a commonality among vampires once transformed, if infected by the same spirit essence. Vampires are as varied in behaviors and thoughts as humans, and most seem to retain most of their human mentality once transformed until they age past a certain point and slough off more and more of the mortal considerations.
3) The vampiric transmission across several lores involves the bite, which often includes sensations such as paralysis ecstasy and painkilling effects (of the puncture wound). Vampire's licks in many lores eliminate a puncture wound altogether, erasing the marks of the vampire's feeding. This indicates very powerful restorative and biochemical processes which the vampire seems to be able to control the transmission of. Many lores hold the subject must be drained of blood near-completely in the formation of a new vampire, others that the mere bite can cause vampiric infection and thus create a new vampire....and that is why those vampires must kill their prey fully when they feed or they create a new vampire each time they feed. Perhaps different strains of vampiric creation similar to differences in other virus behaviors? If the explanation is spiritual there should only be a few (or one) primary methods for transferring a fraction of that spiritual energy to another person to create a new vampire that would work consistently. It just seems a bit too random to be a spiritual influence to me. Another note is that all vampires get stronger as they age, which lends more credence to a viral type infection over a spiritual one, as there shouldn't be a way that strictly feeding upon blood would increase a vampire's ties to a spiritual entity. It would, however, continue to solidify a viral infection in a vampire's body making less human and more powerfully virus over the course of time.
I stand by the conclusion that vampirism is most likely 'intelligent viral' infection. The creation of a new vampire consistently involves draining the victim to the point of near death, and then feeding the victim a mixed quantity of their own blood plus the vampire's own. Resulting death of the meatbag then occurs, and there is enough of the virus present to now 'overwrite' the genetic code of the victim locking it into it's state of when it died. The virus then maintains that genetic structure perfectly with blood as it's primary fuel, thus a vampire doesn't die to old age or disease or even grievous wounds (except the classic 'vampire killers' of sunlight, complete destruction of the body, etc). I suspect that a great deal of concentration must be present in the creation of a new vampire, and that the infecting vampire must be directing the virus actively to overcome and rewrite the new host's body until it achieves control. At that point, the new vampire now is a separate entity and gains it's own control over the virus within it's body when it 'awakens' as a vampire. This also explains why the creating vampire does not lose any strength aside from suffering from a lack of blood at the time of creating a new vampire.
A zombie virus or infection on the other hand spreads swiftly and easily from host to host, transmitted by bites or fluid contact. This performs in a similar behavior to vampiric transmission, except for the fact that the process is NOT intelligently handled. The end result is that the zombies typically possess only the most basic of primal urges and motor control. The body degrades rapidly as it would normally were a corpse left exposed to the elements, so it holds that zombie infection is a dramatically different type than vampiric, much more akin to a conventional virus or bacteria than something more powerful like the vampire's.