Different sources say different things!!!!
In Bram Stoker's Dracula, they are allergic to garlic and holy water and can be killed by driving a stake through the heart!!!!
In the Librarian series they can be staked only if the wood is of a Aspen tree or else can be killed by chopping off the head!!!!!
In both Twilight and Underworld series they are not associated with demons and thus the holy water has no effect on them!!!!In Underworld they possibly have a chapel in their castle!!!!
In Twilight they are killed by burning the pieces of their body!!!!!
In Underworld werewolves are killed by silver knives and bullets and later silver nitrate bullets injecting silver into their bloodtsream!!!!Vampires are killed by chopping off the head or by burning in sunlight or the UV rounds used by the Lycans!!!!
However a sure shot way of killing a werewolf seems to be separating its head and its heart or in other words, tearing off its head!!!!
In PKYEK, both vampires and werewolves can be killed by staking them through the heart!!!!
Here vampires, as shown in True blood series, are allergic to silver as well as incense and sandalwood!!!!
However so far no such weakness of werewolves have been shown!!!!
The reproductive powers of both the species are also not fully revealed at this point!!!!!
Moral of the story is that it keeps changing with every story written or made!!!!!😆