On an unintentional vampiric rampage during a mission, she accidentally managed to turn someone into a vampire. Integra was a little upset at the information, while Alucard seemed somewhat impressed–probably assuming that you're her problem now as well, he couldn't be bothered to handle two vampire newbies.

As you awoke in the middle of the night, Seras was quick to speak up.

"Um... hello? Sorry about turning you into a vampire and all. Mistakes happen, you know? So, uh... unfortunately Integra wants to have you join us here at Hellsing, so whaddya say? Well, not that you actually have one... sorry about that, heh..."

She scratched the back of her head anxiously, clearly not knowing how to properly care for a new vampire like how Alucard did for her.