A vaccine is a biological preparation that contains weakened or killed forms of a microbe, its toxins, or one of its surface proteins (plus many other ingredients, i.e. aluminum or fetal bovine serum), and is meant to stimulate the body’s cells in the immune system, including macrophages, T cells, and B cells.
Vaccination simulates infection in the body, whilst trying to avoid full-blown infection.
In 1796, Edward Jenner took the pus from a cowpox blister on a milkmaid’s hand and scratched it into the skin of his gardener’s eight-year-old son, James Phipps, to see if cowpox offered cross protection against smallpox.
Six weeks after the boy recovered from an acute cowpox infection, Jenner exposed the boy to smallpox material taken from another boy’s arm, Jenner was searching for a safer alternative to “variolation” which was the same process but exposing infants and children to live smallpox via the pus or scab of another person.
Jenner also used his son in his experiments, but he became mentally disabled and died of TB at the age of 21. Thus the world of vaccination was born.