Jenner returned to Berkeley in 1773 to work as a doctor. Soon afterwards he began to investigate cowpox and gradually became convinced that it was efficacious as a protection against smallpox. In 1796 he inoculated James Phipps, an eight-year-old boy, with cowpox matter. Two months later he inoculated Phipps with smallpox and he did not develop the disease.
Jenner described his experiments in his book An Inquiry into the Causes and Effects of the Variolae Vaccinae (1798). Initially vaccination was opposed by the medical profession until over 70 principal physicians and surgeons in London signed a declaration of their confidence in it and within a few years was being used in many parts of the world.
Edward Jenner died in 1823.