Vaccination
Training the immune system with a harmless or weakened version of a germ so the body is ready if the real one arrives.
The immune system learns. After fighting off an infection it keeps memory cells and antibodies that recognise the germ's distinctive surface shapes, so a second encounter is usually defeated quickly, often before you feel ill. Vaccination uses this memory on purpose, giving the body a safe preview of a germ.
An earlier method, variolation, a form of inoculation, was used against smallpox in Africa and Asia long before it was common in Europe. Pus from a person with a mild case of smallpox was put into a small cut in a healthy person's skin, usually causing a milder illness that left lasting protection. In Boston in 1721, after an enslaved African man named Onesimus told the minister Cotton Mather about the practice, the doctor Zabdiel Boylston inoculated hundreds of people. Their records showed that it cut smallpox deaths to about 1 or 2 per cent, from roughly 15 per cent among those who caught the disease naturally.
In 1796 Edward Jenner used material from cowpox, a related but much milder disease, instead. Cowpox is similar enough to smallpox that the immunity it triggered protected against both, without the risk of passing on smallpox itself. The word vaccine comes from the Latin vacca, a cow.
A common misconception is that variolation and vaccination are the same thing. Variolation used the real disease; vaccines use a weakened, killed, related or partial form of the germ.
Coming up in future stories
- He Caught Yellow Fever, Then Tamed It 1930s–1951 · Rockefeller Foundation, New York; Max Theiler, from Pretoria
- How Bangladesh Found the Last Case of Deadly Smallpox October–November 1975 · Kuralia village, Bhola Island, Bangladesh
- Rio Rioted for a Week Against Smallpox Vaccines 10–16 Nov 1904 · Rio de Janeiro, Brazil
- The Lab Doctor Who Broke the Rules to Find Nipah Sept 1998 – 1999 · Perak and Negeri Sembilan, Malaysia