The smallpox virus appears to have been with humanity for millennia before a global vaccination drive wiped it out. Current genome research suggests how smallpox spread and where it came from.
The smallpox vaccination used calf lymph, which was unacceptable to vegetarians and anti-vivisectionists who were growing in number from the mid 19th century.
Director of the National Institute for Health Research (NIHR) Health Protection Research Unit in Emerging and Zoonotic Infections, and Professor of Neurology, University of Liverpool