Okay, I'm here to fill in some of the religious/mythological side of why traditionally these beings had certain weaknesses, which might maybe help...
So first off, Werewolves and Vampires kinda used to be the same monster, or interchangeable, in european folklore. This is why older vampire stories, vampires are often shapeshifters, able to turn into bats, but also things like wolves, giant cats (like Carmilla) etc. And also having control over animals associated with the night or with being predators or vermin; rats, wolves etc.
Over time, the two diverged into separate monsters, but this is why they share some common weaknesses, most notably silver. In Caribbean mythology, the Lagahoo, derived from Loup-Garou, is a type of undead; a wicked soul risen as a shape-shifting monster, and needs to be drenched in holy oil, which preserves some of that old crossover between Vampires and Werewolves.
Why in mythology are monsters weak to silver?
This is a really interesting one, and it's linked to the term "impure" or "corrupted" and Christianity. In Christianity, the concept of purity is very important, and so the metals gold and silver kind of have a holiness to them, because even a long time ago, they could be refined to a high level of purity, and when they were pure, it was visible in them being shinier and less likely to tarnish. So the idea was, that because the gold or silver was very pure that that inherent purity would hurt something impure.
This is also why vampires don't appear in mirrors, which used to be a sheet of glass with silver on the back.
A lot of these monsters weaknesses are linked to things that are seen as holy or cleansing. Vampires can't go out in sunlight (ie. the light of God) and Werewolves only wolf out in darkness for similar reasons. Vampire can't cross running water in some myths, because again, running water washes sins away in Christian mythology, and originally baptism would have been done in rivers.
That said, it is true that silver really does have anti-bacterial properties, and there is legit research into using silver to treat various illnesses at the moment. And also light. There's research into using lasers to blast cancerous cells, and we know sunlight can treat various illnesses.
Plus running water is generally safer to drink than still water, and washing is a good way to stay healthy... so a lot of these things have a basis in reality.
Garlic too! Though in Dracula, it wasn't garlic bulbs, but wild garlic flowers that Van Helsing used to deter vampires. Still, garlic has antibacterial properties and numerous health benefits, and has been used as a remedy for illnesses for centuries.
So maybe if Vampirism or Lycanthropy is a virus or a sickness, the weakness to silver, sunlight, garlic and running water; all things that can be beneficial in the treatment of illness, kinda makes sense.
Fire is a common weakness of monsters, because people know animals are scared of fire and that fire is a good way to kill off germs and things. Again. there's that link of burning away unclean things, light that scares away monsters etc.
The stake through the heart originally wasn't to kill the vampire, it was to pin it into the coffin, so it couldn't leave. Originally, people thought that vampires would go back to their coffin every day, and just get out of it at night and wander around. They were often blamed for outbreaks of illness. Why not just burn the body? Because in Christianity, it's traditionally believed that you'll need that body later, because on Judgement day, everyone gets up out of their coffins and goes to party with Jesus (and also everyone will be like thirty, regardless of how old they were when they died... I dunno, old Christian mythology is wild), so burning a body was seen as a big no-no, and instead they'd do things like cut the head off, pin the body into the ground with a stake, scatter rice grains around, so the vampire would stop to count them all (this is a real vampire weakness in mythology...).
Finally... probably worth mentioning that many of the traits associated with vampires do exist in a real medical condition.. It can cause things like light sensitivity, unusual hair growth, receding gums that make teeth look longer, aversion to garlic etc. That said, most people believe a lot of the traits we associate with vampires are actually more likely to come from Christian mythology and how the decomposition process can sometimes cause a body to appear to have gained weight, have a rosy complexion, blood coming from the mouth, hair and nail growth and elongated teeth (actually receding gums and scalp or nail beds).
