IV.

Early Efforts Against Smallpox

Early attempts to prevent smallpox originated in China several thousand years ago. In the ancient process known as variolation, dried smallpox scabs were blown up the nose of the patient. Later, the procedure took the form of scratching the arm with a needle containing pus from a smallpox lesion. Used before scientists fully understood infectious diseases and immunology, variolation was dangerous and resulted in full-blown smallpox in 2 to 3 percent of cases. But in skilled hands variolation induced a mild infection that stimulated the production of antibodies, creating effective immunity against smallpox for several years. The practice gained popularity in both Europe and North America during the 18th century.

A more effective medical blow against smallpox, and one of history’s landmark biomedical achievements, took place in 1796 with an experiment performed by the British physician Edward Jenner. He had observed that young women who milked cows for a living often contracted a minor skin infection known as cowpox—and that these milkmaids subsequently seemed to be protected from smallpox. Jenner arranged to perform an experiment on eight-year-old James Phipps, scratching his arm with pus taken from the cowpox lesion of a milkmaid. Six weeks later, when Jenner scratched Phipps's arm with pus from a smallpox lesion, the boy failed to show any reaction or illness. The cowpox virus had created natural immunity against smallpox while carrying none of the risk posed by variolation with actual smallpox virus. Jenner was apparently not the first to attempt this procedure, but he was the first to approach it scientifically and to document and publish the results. Thus, with this new procedure, which was later dubbed vaccination (from the Latin word vacca for 'cow'), Jenner set the course that ultimately led to victory over smallpox.

The practice of vaccination did not catch on quickly, however. Some people refused the smallpox vaccine, offended by the idea of introducing matter from an animal into their bloodstreams. Others believed that a vaccine would interfere with God's will. Vaccination gradually gained acceptance and became more widely practiced.

Even after smallpox vaccination had become standard in the developed world, epidemics continued in some regions. Between 1900 and 1920 in India, for example, smallpox killed an average of 370 out of every 100,000 people in the population every year. In all, smallpox killed an estimated 300 million people in the 20th century.

In the battle against smallpox in the 20th century, two weapons were key: (1) an effective vaccine and (2) the fact that the smallpox virus exists only in humans. Unlike strains of the influenza virus, for example, which can exist in domestic fowl or pigs before jumping to humans and causing flu outbreaks, smallpox requires a chain of human hosts to keep its life cycle going. Following infection, a host falls sick and will either recover or die, but by then the virus will have moved on, renewing itself by being spread to other human hosts who have contact with the infected person. Ultimately, the strategy against smallpox was to break this chain of infection forever.