One of History's Deadliest Diseases
Smallpox was caused by the variola virus. It spread mainly through long face-to-face contact with an infected person. It started much like flu, with fever, headache and muscle pain. Then sores appeared in the mouth, followed by a rash that turned into fluid-filled blisters.
About 30 percent of people who caught it died, and the death rate was even higher among babies. Many survivors were left with deep scars, and some went blind.
Its history is long. The earliest physical evidence of smallpox comes from Egyptian mummies of people who died some 3,000 years ago. In 18th-century Europe, it killed an estimated 400,000 people a year, including five reigning monarchs, and caused a third of all blindness.
When it reached the Americas and Australia, where people had never faced it before, it killed huge numbers and helped pave the way for conquest. In the 20th century alone, it is estimated to have killed up to 300 million people.
Help From a Cow
People fought back long before modern medicine. One early method was inoculation, deliberately giving someone a small dose of smallpox to protect them, appears to have started in China around the 1500s. Europe picked up the practice from Asia in the first half of the 18th century.
The big breakthrough came in 1796. The British doctor Edward Jenner showed that infecting someone with cowpox, a much milder disease, protected them against deadly smallpox. It was the first vaccine ever developed against a contagious disease.
That is where the word itself comes from. Vaccine comes from vacca, the Latin word for cow. Jenner called cowpox variolae vaccinae, meaning smallpox of the cow.
There is a twist. In 1939, scientists showed that the virus used in the modern smallpox vaccine was actually different from cowpox. It is now known as vaccinia, and genetic studies show it is most closely related to horsepox.
The Campaign to Wipe It Out
Even with a vaccine, smallpox did not go away quickly. In the early 1950s, there were still an estimated 50 million cases a year. As recently as 1967, 15 million people caught it and two million died.
That year, the World Health Organization stepped up a global vaccination campaign. The disease had weaknesses that made it beatable. It was not spread by insects or animals, and people could not carry it without showing symptoms. It mostly spread after the rash appeared, which made cases easier to spot.
The last naturally occurring case was diagnosed in October 1977. In 1980, the World Health Organization officially declared smallpox eradicated.
It remains the only human disease ever wiped out this way. Only one other infectious disease has been eradicated: rinderpest, a disease of cattle and similar animals, declared gone in 2011.
Two Samples Left
Smallpox did not quite disappear on schedule. The final known death came in 1978, from a laboratory in Birmingham, England.
Today, only two live samples of the most dangerous form of the virus are known to exist. One is kept at the CDC in Atlanta, in the United States, and the other at the Vector Institute in Koltsovo, Russia. Any research on them has to be approved by the World Health Organization.
Because of fears that the virus could be used as a weapon, the vaccine is still made for research and protection. It has found a new use, too: smallpox vaccines have been approved in some countries to help prevent mpox, a related disease.
Over the centuries, smallpox touched famous lives. It affected the ancient Egyptian ruler Ramses V, the composer Wolfgang Amadeus Mozart and the American president George Washington. Between 65 and 80 percent of survivors were left with lasting white scars.
