Homosapien transitition from hunter-gather to farmer and animal herder likely accounts for the origins of the smallpox disease. The earliest signs of its presence came from the mummies of ancient Egypt. The disease afflicted commoner and ruler alike — the remains of Egyptian pharaoh Ramses V bore signs of the disease. Pre-modern Europe fared little better — anywhere from 20 to 60 per cent of those afflicted died, and survivors were left with disfiguring scars at best and blindness at worst. It could have continued indefinitely if not for the perseverance of a small boy named Edward Jenner.

On this day, May 14, 1796 Jenner made the first experimental smallpox vaccine injection. He had heard for years that dairymaids were immune to smallpox due to their exposure to cowpox, and decided to test out that theory, injecting a sample taken from a cowpox-afflicted dairymaid Sarah Nelms into a healthy child. His predictions proved correct: after briefly suffering flu-like symptoms, the boy improved and developed immunity to smallpox.

Inoculations were nothing new at the time, and Jenner himself received one as an eight-year-old. His breakthrough was in proving scientifically they work, and convincing the rest of the world of the same. As the British intellectual Francis Galton noted, “In science credit goes to the man who convinces the world, not the man to whom the idea first occurs.”