A kind of Terry Pratchett, Good Omens version, absolutely. "We don't actually have to make new plagues, we just convince enough people that the natural plagues they've already got don't exist, or the causes aren't what they've been told, or that the treatments do greater harm than the disease. In fact, we don't even have to deceive that many. A handful of posts to alternative medicine, conspiracy, and mom's net forums, and human nature will do the rest."