Smallpox is a deadly disease caused by the variola virus. From ancient Egypt and Greece, to China and the Americas, it has killed countless millions for centuries. Smallpox arrived in the New World with Columbus and Cortes, and it devastated Native American populations who had no immunities to the virus. The disease played a major role in the conquest of Mexico and Peru, as well as the European settlement of North America. In India there is even a goddess of smallpox, Sitala. Her name means “the cool one.” If you are a virologist, perhaps you might think variola is pretty cool. But rest assured, smallpox is a lethal disease that has played no small part in human history.

Variola is one of the largest and most complicated viruses known. It invades a human cell and forces it to reproduce the virus until there are thousands of viruses inside the cell. The cell bursts and showers the virus onto other cells. The disease is horrible, causing high fever, red pus-filled blisters and oozing sores.

It is transmitted very quickly by a cough or a sneeze. Infection occurs by inhaling these airborne particles or by touching contaminated clothing. As recently as 1967, 15 million people contracted smallpox. Thankfully one of modern medicine’s true triumphs has been smallpox’s eradication. In 1980, after a global campaign of vaccinations and surveillance, the World Health Organization made an astonishing announcement: smallpox is dead. Today the smallpox virus only exists frozen in laboratories where it can be studied. There is still no known cure...