© Jean-Loup Charmet/Science Photo Library
A doctor peforming a smallpox vaccination on an infant, after a painting of the nineteenth century.
A doctor peforming a smallpox vaccination on an infant, after a painting of the nineteenth century.
The development of vaccination highlights the importance of applying proper scientific methods, including carefully controlled experiments, to the investigation not just of natural phenomena but to pieces of folk wisdom, which sometimes have a basis of truth. William Gilbert (see here) proved that the folklore story that garlic will demagnetise a compass needle was false; but Edward Jenner showed that the folk medicine preventative for smallpox actually worked. He thereby established the scientific basis of vaccination.
Before the development of an effective vaccine, smallpox was one of the main killer diseases. It is actually two related diseases, caused, we now know, by one of two viruses, Variola major and Variola minor (the name derives from the Latin varius, meaning spotted; victims are covered in small blisters which burst leaving pock marks on the skin). The ‘minor’ form is less dangerous to life than the ‘major’ form, but according to Voltaire, writing in 1778, about 60 per cent of the European population caught one or other form of the disease, and a third of the victims died as a result. The World Health Organisation estimated that as recently as 1967 some 15 million people contracted the disease, and two million of them died. As with many infectious diseases, mortality was worse among infants. Because the disease was so prevalent and so serious, before a vaccine was developed people had tried desperate remedies to prevent it. In some parts of the world, people had tried scraping bits of scab from the healing spots of someone with a mild form of smallpox into their skin in the hope that this would somehow make them immune. It seemed to work, and, although some people died as a result of this self-treatment, the practice was brought to England from the Middle East in 1721 by Lady Mary Montagu, the wife of the British Ambassador to Turkey.
Alongside this folk remedy, country lore said that milkmaids were less likely than other people to get smallpox, and this was thought to be linked to the fact that, as a result of their work, they often caught a much milder, but related, illness called cowpox. In the second half of the eighteenth century, several investigators across Europe tested the idea on an ad hoc basis by deliberately infecting people with cowpox. But nobody carried out a proper scientific experiment to prove the connection between cowpox and smallpox until Edward Jenner took up the challenge.
Jenner was a country doctor who became completely convinced that catching cowpox provided immunity from smallpox. To prove this, in 1796 he carried out an experiment which seems alarmingly cavalier to modern eyes. He took pus from the blisters of a milkmaid called Sarah Nelmes, and injected this into an eight-year-old boy, James Phipps, who was the son of Jenner’s gardener. We do not know what inducement the boy or his father were offered. James developed cowpox, but soon recovered. Jenner then injected the boy with smallpox. He did not develop the disease. Jenner described the experiment in a letter to the Royal Society, but was advised, absolutely correctly, that a single example was not enough to prove his case. So over the following months he carried out a series of similar tests on 23 other people, including his own 11-month-old son. This was enough to persuade the Royal Society, which published the resulting paper in 1798. Jenner coined the word vaccine (from the Latin ‘vacca’ for cow), and the term later became applied to any use of deliberate injection of a weakened or dead form of a virulent organism to provide immunity from the strong form of the disease.
The medical community was slow to respond to Jenner’s discovery, and he gave up his medical practice to concentrate on further research and the promotion of vaccination. Among other things, he developed a method of taking material from human cowpox pocks and drying it onto glass so that it could be taken to where it was needed. In 1853, vaccination against smallpox was made compulsory in Britain, and as the technique spread, together with other efforts to stamp out the disease, smallpox became increasingly rare. In 1801, Jenner had published a pamphlet about vaccination which said, ‘the annihilation of the Small Pox, the most dreadful scourge of the human species, must be the final result of this practice’. It took nearly 180 years to achieve that goal, but by the end of the 1970s the World Health Organisation was able to declare that smallpox had been eradicated. The virus now exists only in two government research laboratories, one in the USA and one in Russia, under supposedly secure conditions. Most people think it would be better to destroy these remaining samples.
The important message to take away from this story, however, is not just that Jenner inoculated people with cowpox in order to prevent them catching smallpox. Other people had done that already. The difference is that Jenner then established by experiment (somewhat alarming experiment!) that they were immune to smallpox, and did so repeatedly with enough different subjects to prove his case.