Along with Vampires, you also get Plasma plants and Garlic bulbs. Leave a couple of garlic bulbs on the ground near your front door, or you can make a garland or wreath of garlic and hang it on a wall. Vampires get all nauseous. They really don't like it.
I've bred and evolved Garlic up to Perfect level plants - it takes a while, but perfect produce is looked upon favourably by Sims who receive it as a gift. So I have been giving it as a friendly gift to known Vampire Sims. They carry it around with them, and their poor confused Sim brains can't work out why their vampire powers won't work, and why they keep throwing up. Good times.
I'm quite happy with my purchase of the Vampires pack. If it is available on sale, it might be worth picking up. There's some good CAS and Build mode stuff too.