When the first COVID-19 vaccines were approved for emergency use last December, it felt like - at last! - our nightmare was nearly over. Then came reports of botched distribution efforts, from broken websites to factory mix-ups. Scientists created the vaccine in record time, but it was beginning to look like that might’ve been the easy part.

But if you think vaccine distribution was a logistical nightmare in 2021, try doing it in the early 1800s. In 1796, Edward Jenner discovered that cowpox worked as a vaccine against smallpox. All you had to do was pop a cowpox sore on someone’s skin and transfer the lymph fluid (a.k.a. pus) into a cut on a second person. Soon, they'd develop a few sores, but when they recovered, they'd be immune to smallpox, a far more serious disease.

This worked well enough for short distances, but when smallpox began to destroy Spanish colonies in the Americas, Spain had to figure out a way to move the vaccine across the ocean. Their solution was resourceful, effective, and very ethically dubious. Science writer Sam Kean brings us the story of the world's first vaccination campaign.

Sam Kean is a science writer, author of The Bastard Brigade, and host of the podcast Disappearing Spoon from the Science History Institute.

Listen to our episode on the origin of the word ‘vaccine.’

Listen to a full episode about this story on Sam Kean’s podcast, Disappearing Spoon.

Science Diction is produced by Johanna Mayer and Elah Feder. Elah is our Editor and Senior Producer. Daniel Peterschmidt is our composer. Nadja Oertelt is our Chief Content Officer.