Harry Potter Faces a Biohazard Crisis

I saw a Harry Potter and Resident Evil fanfic called "When Harry Potter Meets Resident Evil" on Baidu Tieba, but the author only wrote three chapters and never continued. So I got the itch to write my own. I know, I'm guilty of starting stories and never finishing them. Forgive me, I just can't help myself. Note: Professor Snape didn't die at the final battle in this story. He was rescued, but went into hiding, and everyone was told he had died. I've always resented the professor's death in the original, so I'll be making a few changes here.