How did a vaccine cross oceans before refrigeration?

In 1803 people worked desperately to keep a chain of vaccinations from breaking. A hundred and seventy years later they were working just as hard at the opposite: finding smallpox's last chain of transmission, and cutting it.

What you will follow

This guided story moves the same world map through 12 sourced scenes. It begins at the opening rather than dropping you into an unexplained year.

How to read the map: The map uses discrete, approximate border snapshots. A narrated year may use the closest available snapshot, and schematic arrows show relationships rather than precise routes.

Related subjects on the map

• Vaccination and the eradication of smallpox
• Transatlantic slave trade
• Cold War

Sources used by this story

1. World Health Organization, “History of smallpox vaccination.”
2. World Health Organization, “A Brief History of Vaccination.”
3. Frank Fenner et al., Smallpox and its Eradication (Geneva: World Health Organization, 1988).
4. Michael Bennett, War Against Smallpox: Edward Jenner and the Global Spread of Vaccination (Cambridge: Cambridge University Press, 2020).
5. Catherine Mark and José G. Rigau-Pérez, “The World's First Immunization Campaign: The Spanish Smallpox Vaccine Expedition, 1803-1813,” Bulletin of the History of Medicine 83, no. 1 (2009): 63-94.
6. J. Z. Bowers, “The Odyssey of Smallpox Vaccination” (the “warm chain”), Bulletin of the History of Medicine 55 (1981).
7. Carlos Franco-Paredes, Lorena Lammoglia and José Ignacio Santos-Preciado, “The Spanish Royal Philanthropic Expedition to Bring Smallpox Vaccination to the New World and Asia in the 19th Century,” Clinical Infectious Diseases 41, no. 9 (2005): 1285-1289.
8. D. A. Henderson, “Smallpox Eradication — A Cold War Victory,” World Health Forum 19, no. 2 (1998): 113-119.
9. Stanley O. Foster et al., “Smallpox Eradication in Bangladesh, 1972-1976,” Vaccine 29, supplement 4 (2011): D22-D29.
10. US Centers for Disease Control and Prevention, “History of Smallpox.”
11. Slave Voyages, Trans-Atlantic Slave Trade Database, 2019 edition.