Editor’s Note: This is the first installment in a 12-part series of articles on vaccinations of horses.

Of all the medical advances in the past couple of centuries, the one that might be the most remarkable is also the one we’re most likely to take for granted. The simple pinprick of an intramuscular injection taking less than 10 seconds protects our families, our pets, our horses, and ourselves from diseases that once meant certain death. In a flash, there are no more worries about the horrors of diphtheria, rabies, tetanus, or equine encephalomyelitis. All from a few ccs of vaccine.

Perhaps we are so casual about vaccination because it’s so familiar. In grade school, most of us learned the story of Edward Jenner, who in 1796 deduced that milkmaids exposed to cowpox, a relatively benign disease, seemed to be immune to the far more virulent smallpox. Jenner might in fact have been borrowing knowledge from more ancient sources–there is some indication that medical practitioners in the Middle East had known for centuries how to immunize patients against smallpox with a small amount of pus from a cowpox vesicle.

Smallpox, which had wreaked untold misery on the human race for millennia, became the first disease against which humans were immunized–and in the 20th Century, the first disease to be officially eradicated from the face of the earth