How did smallpox get to the New World if smallpox patients would be too sick or unfit to be on the ships and most people would have had smallpox when they were children?

by JarJarAwakens

I'm specifically interested in the early Spanish and Portuguese colonization before widespread immigration.

misyo

Humans can be asymptomatic carriers of diseases without being infected by the diseases. Smallpox wasn't always an extreme case with 100% mortality rates among Europeans either- it's very possible for someone to develop a more mild case of smallpox during the Atlantic crossing and survive, mostly due to antibodies built up in European immune systems over dozens of generations. Also, much like chickenpox, if someone had a mild case of smallpox as a child, they can get smallpox again as an adult.