By the mid-18th century, smallpox was a major endemic disease everywhere in the world except in Australia and small islands untouched by outside exploration. In 18th century Europe, smallpox was a leading cause of death, killing an estimated 400,000 Europeans each year. Up to 10 percent of Swedish infants died of smallpox each year, and the death rate of infants in Russia might have been even higher. The widespread use of variolation in a few countries, notably Great Britain, its North American colonies, and China, somewhat reduced the impact of smallpox among the wealthy classes during the latter part of the 18th century, but a real reduction in its incidence did not occur until vaccination became a common practice toward the end of the 19th century. Improved vaccines and the practice of re-vaccination led to a substantial reduction in cases in Europe and North America, but smallpox remained almost unchecked everywhere else in the world. By the mid-20th century, variola minor occurred along with variola major, in varying proportions, in many parts of Africa. Patients with variola minor experience only a mild systemic illness, are often ambulant throughout the course of the disease, and are therefore able to more easily spread disease. Infection with v. minor induces immunity against the more deadly variola major form. Thus, as v. minor spread all over the US, into Canada, the South American countries, and Great Britain, it became the dominant form of smallpox, further reducing mortality rates.
As recently as 1967, 15 million cases occurred a year.Inoculation for smallpox appears to have started in China around the 1500s. Europe adopted this practice from Asia in the first half of the 18th century. In 1796, Edward Jenner introduced the modern smallpox vaccine. In 1967, the WHO intensified efforts to eliminate the disease. Smallpox is one of two infectious diseases to have been eradicated, the other being rinderpest in 2011. The term "smallpox" was first used in Britain in the early 16th century to distinguish the disease from syphilis, which was then known as the "great pox". Other historical names for the disease include pox, speckled monster, and red plague. Classification
There are two forms of the smallpox virus. Variola major is the severe and most common form, with a more extensive rash and higher fever. Variola minor is a less common presentation, causing less severe disease, typically discrete smallpox, with historical death rates of 1% or less. Subclinical (asymptomatic) infections with Variola virus were noted but were not common. In addition, a form called variola sine eruptione (smallpox without rash) was seen generally in vaccinated persons. This form was marked by a fever that occurred after the usual incubation period and could be confirmed only by antibody studies or, rarely, by viral culture. In addition, there were two very rare and fulminating types of smallpox, the malignant (flat) and hemorrhagic forms, which were usually fatal.