Some reassuring news - Vampires don’t exist. The Maths prove it.
"Let us assume that a vampire needs feed only once a month. This is certainly a highly conservative assumption, given any Hollywood vampire film. Now, two things happen when a vampire feeds. The human population decreases by one and the vampire population increases by one. Let us suppose that the first vampire appeared in 1600 c.e. It doesn’t really matter what date we choose for the first vampire to appear; it has little bearing on our argument. For January 1, 1600, we will accept that the global population was 536,870,911.2 In our argument, we had at the same time one vampire.
We will ignore the human mortality and birth rate for the time being and only concentrate on the effects of vampire feeding. On February 1, 1600, one human will have died and a new vampire will have been born. This gives two vampires and 536,870,911–1 humans. The next month, there are two vampires feeding, thus two humans die and two new vampires are born. This gives four vampires and 536,870,911–3 humans. Now on April 1, 1600, there are four vampires feeding and thus we have four human deaths and four new vampires being born. This gives us eight vampires and 536,870,911–7 humans.
By now, the reader has probably caught on to the progression. Each month, the number of vampires doubles, so that, after n months have passed, there are 2323 … 32=2n times vampires. This sort of progression is known in mathematics as a geometric progression—more specifically, it is a geometric progression with ratio two, since we multiply by two at each step. A geometric progression increases at a tremendous rate, a fact that will become clear shortly. Now, all but one of these vampires were once human, so that the human population is its original population minus the number of vampires excluding the original one. So after n months have passed, there are 536,870,911–2n+1 humans. The vampire population increases geometrically and the human population decreases geometrically.
We conclude that if the first vampire appeared on January 1, 1600, humanity would have been wiped out by June of 1602, two and a half years later. “