All pop culture characters, heroes and villains, have their weaknesses. Even Superman has kryptonite, which is really not enough to make him interesting. Vampires are terrifying, but can be defeated by several things: sunlight, garlic, religious symbols, decapitation, or a stake through the heart. I would also posit that a complete dental extraction would work, although that would be difficult to arrange. In a certain case, even a reflexive action you aren't even totally aware of could be enough.
And these two people will go on about their evening never knowing that she killed a vampire, and saved their lives by a simple prayer she put no thought into at all. Unless he had the presence of mind to say, "Why did you bless yourself after you sneezed?" To which she would reply "I didn't sneeze; I though you sneezed!" Then they look around to find no one there and decide it would be best to turn the house lights on. That's one reason I'm not a comic artist, as my stories would go on way longer than necessary. This comic is from Chris Allison at Toonhole. -via Geeks Are Sexy