Religion Plays an Imported Role in Dracula.
Dracula and the other vampires in the book are clearly portrayed as devil like creatures. With their burning red eyes. The world of vampires is on large part based on an assumption in the existence of a god or something god like. So this begs the question would a vampire be vulnerable to other symbols of faith, like the Star of David or pagan symbols? Christianity was the dominant religion at that time/place, so it’s never made clear if other religion symbols would work at repelling vampires. Van Helsing is a catholic and, many of the vampire “repellents” he use come from that faith, through as Christianity is closely tied with Catholicism the symbols, are peasants . Stoker never explores the idea of other religious symbol working, but for the time and place, when the only other religion is Judaism, and that is looked down upon. You could not expect him too.
No One is Safe
An imported character trait of mina is her being very Religionist and pure. Bram stoker did this deliberately to accentuate her dissent in to vampire hood and thus impurity and evilness. We see that Dracula can touch and taint even the purest among us.
Why The Garlic?
Garlic was associated with health and considered a remedy. There is also a theory that with vampires heighten senses, the smell was too much for them. As far as actually knowing the reason why it was used I don’t know. It could be for one of the two reason above or for something very different like the old wives tale that Garlic repels Mosquitoes.