Personally, I really don't care if they can get sick or not. The only frustrating part was I didn't realize that vampire sims can take the medicine. Both of my sim vampires have the withered stomach weakness and can't eat normal human sim food and drinks or they'll get sick. It wasn't until I read this post I found out that they can take the medicine and not get sick. It really is strange that the vampires can get sick and take normal human sim medication. But it's not a huge problem for me, as long as I can have them take the medicine it's fine. But I would still want it to be fixed if it is a bug.