As long as there have been English people in America, there have been vampires. (Who knows, maybe the Vikings brought them over. Though we think they're more likely to bring werebears.)
Here's the story that Henry tells Abe about how he came to America to start a new life, and was made into a vampire (which is certainly a type of new life):
There were 117 people who came over to America to found an English colony in 1587, and there will be a quiz on all of them. No, that's not true, because only a few of these people get mentioned in this story and 1587 is a long time ago.
John White is one of the most important members of the colony, since he's the leader of the expedition and its only survivor. After they start the colony, John White heads back to England to get some reinforcements. But he can't make it back for three years and by the time he does, the Roanoke colony has all disappeared. We're assuming this haunts White for a while. It would haunt us, because when he gets back, this is what he finds:
Gone. His colony had simply vanished into thin air. The buildings remained exactly as they had been (though weather-beaten and overgrown). Tools and supplies were exactly where they belonged. Surrounded by rich soil and abundant wildlife, how could they have starved? If there was some kind of pestilence, where were the mass graves? If there was a battle, where were signs? It didn't make any sense. (3.129)
This is a total mystery for us, but not for Henry, since Henry knows all about Dr. Crowley, vampire. Crowley is a beloved member of the crew, but he's also been killing a few of them in order to feed. On the trip from England, Crowley killed one sailor and made it look like an accident; and killed a young girl and made it look like she jumped overboard. And then when he's in America, Crowley kills another guy and makes it look like the natives did it. Crowley would probably continue to kill a little and disguise it, but someone catches him and so he has to kill everyone except for a baby and Henry.
That baby is Virginia Dare, the first English baby born in America. She's famous, but in this book, she's vamp chow. That is, Crowley doesn't want to kill Virginia at first:
Crowley had hesitated to kill Virginia Dare. A baby that he had personally delivered? The first English soul born in the New World? These things had sentimental value. Besides, she would have no memory of what had happened here, and a young female companion might prove useful in the lonely years to come. (3.143)
Ick. In any case, once Crowley finds that Henry is alive, he just decides to eat Virginia now. We suppose that the idea of dealing with a screaming baby is too much for even a vampire. They may be horrible, but no one likes dealing with dirty diapers, not even monsters.