I've only watched Hellsing Ultimate. The Major recognizes Seras as a real threat when he warns Zorin before attacking Hellsing's manor. He calls her a miracle of sorts.
Sure enough, she's clearly stronger than most other vampires. But why? Was it simply the fact that Alucard himself transformed her? What made her special if she didn't even consume Alucard's blood? Why does the Major think so highly of her?
Here is what makes her special. Unlike other vampire who run around just killing random people and do what the want, Seras works for Hellsing, they have a reputation for dealing with stuff like the supernatural. Not to mention (as far as we know) She was the first person to be turned by Alucard(if any other people have been turned they were never mention nor brought up in Hellsing's brief run). He considers her a miracle cause she is most likely the only person who Alucard has never killed(via bites anyway). Or transformed, everyone else is good as dead.
She is special cause she is Alucard's pet, his side kick and almost as dangerous as he is.
