Vampires seem to have a lot of weaknesses. This is because many cultures and histories have been combined and act as a pool to draw from. But in a fantasy world, how can one explain all these weaknesses for what is supposed to be a terrible creature of the night? You could go with the WoD concept and have many types or bloodlines of vampires, or do something simple. The Gods.
Vampires, as with all undead, are weak to holy symbols and Clerics are well tuned to fighting them. Vampires are also killed by sunlight, which is a common weakness they all share, potentially an ancient bane given to them from the God of the Sky. Holy symbols are usually made out of silver, gold, or some other precious resource. Holy water also works as a sort of direct weapon against evil. Vampires can also be destroyed by direct damage and martial might, but so can anything in a high fantasy world. However, even with these powers, the Gods knew that vampires were too dangerous and powerful for mortals to clash with. With dark magic, shapeshifting, mind control, as well as superhuman strength and toughness; Vampires are the natural predators to mortals. In response, the Gods began to grant their followers new weapons against these dark forces; the banes.
Side Note- In some worlds, such as Goblin Punch's Centerra, Gods are very regional. Knowing the Gods of the region is as paramount to traveling through as is knowing the language and having a map. Using this concept, the vampires are instead cursed by the God's bane in their land.
|Graf Orlok @MitchGrave
Once a vampire is cursed, they suffer the Gods bane. The vampire will suffer the bane of that specific priest's God, or if unaffiliated, a random bane is rolled on the table below.
Bane of the Vampires Table – Roll 1d10
 God of Craftsmen – Silver. Silver weapons or items deal more damage, similar to a werewolf.
 God of the Hunt – Wolfsbane. Similar to a werewolf.
 God of Fire – Fire. Regular fire catches on the vampire, dealing 1d6 per round.
 God of the Dead – Vampire must sleep in their native soil. This only makes the vampire weaker instead of killing them, but degenerate their HD by -1. Symbolic of returning to the grave.
 God of the Ocean – Running water. Rivers that flow to the ocean are impassable.
 God of the Hearth – Cannot enter a house invited.
 God of Farming/Fertility – Garlic. The vampire is repelled by it, as though turned.
 God of the Moon – Mirrors. Vampires don't shed a reflection, but a vampire with this bane are additionally turned by the sight of a mirror.
 God of War – Stake through the heart causes instant death. Normal vampires are usually killed by a wooden stake simply due to the damage taken, but this bane guarantees it.
 God of Merchants – Counting. The Vampire is forced to count out beans or grains of rice spilled on the ground; giving enough time to avoid their attack.