In both the world of Dracula and in 1930s Maycomb of To Kill a Mockingbird, a hidden poison erupts and threatens the health and stability of the community. In Dracula, it is the arrival of Count Dracula and a group of his vampires into London, the center of a British empire that at that time spanned the globe. Dracula is treated by Harker and the other protagonists exactly like a virus that must be eradicated. Dracula himself hopes to spread his vampirism across the globe as if it is a virus.
Harper Lee shows that racism is a poison that warps white people's judgment and moral sensibility. The white citizens of Maycomb would rather see an innocent black man convicted of a crime that he didn't commit than upset the racial apartheid of the South. The people of the town condemn, rather than applaud, Atticus for doing the right thing in defending Robinson to the best of his ability. As with the vampires, the disease of Maycomb's racism becomes potentially deadly, in this case to an innocent child like Scout, when she is attacked in her Halloween costume simply because her father stood up for a black man.