Read this excerpt from "Edward Jenner and the History of Smallpox and Vaccination.” Scientific advances during the two centuries since Edward Jenner performed his first vaccination on James Phipps have proved him to be more right than wrong.

Which is the author’s central claim in this excerpt?

Jenner performed his experiments very long ago in a different kind of world.
There have been important scientific advances in the past two centuries.
Jenner’s work is still relevant and important today.
Few changes are needed to improve the vaccination.