Nevertheless, inoculation was not always a safe process; inoculates developed a real case of smallpox and could infect others. The inoculation resulted in a "small number of deaths and complications, including serious infections." Subsequently, Edward Jenner, who was 13 years old when Lady Mary died in 1762, developed the much safer technique of vaccination using cowpox instead of smallpox. Jenner's method involves "engrafting lymph taken from a pustulate of cowpox on the hand of a milkmaid into the arm of an inoculate." Jenner first tested his method on James Phipps, an eight-year-old boy, and when Phipps did not have any reaction after the procedure, Jenner claimed that his procedure "bestowed immunity against smallpox." Then, after spending the next few years experimenting his new procedure, he discovered that his hypothesis was correct. As vaccination gained acceptance, variolation gradually fell out of favour. In May 1958, during the 11th World Health Assembly at WHO Headquarters in Geneva, V.M. Zhdanov, a well-known virologist and epidemiologist who was the Deputy Minister of Public Health of the Soviet Union, proposed a program for global smallpox eradication, and substantiated its feasibility. In 1967 the World Health Organization embarked on a worldwide campaign to eradicate smallpox, which was certified as having succeeded in 1979. Lady Mary Wortley Montagu's introduction of smallpox inoculation had ultimately led to the development of vaccines, and the later eradication of smallpox.