That’s the only question that really matters, isn’t it? Remember in “Goblet of Fire” that Dumbledore gets a “gleam of something like triumph” in his eyes when Harry tells him that Voldemort used a drop of Harry’s blood to revive himself. Rowling calls the gleam “extremely significant.” Perhaps, like his scar, giving blood to Voldemort somehow protects Harry. Who knows?
Well, J.K. Rowling does. The rest of us will just have to wait and wonder.