Smallpox is an acute, febrile, contagious disease caused by the variola virus, which is a member of the family Poxviridae. Until the 1970s, smallpox had been a pandemic disease for more than 3000 years, endemic in tropical and developing areas and occasionally epidemic around the world.
In the past century alone, this virus killed more than half a billion persons, and survivors were left disfigured with pockmarks, sometimes even blind. In large cities, it was a childhood disease that infected virtually every child with a mortality rate of 30%. Thus the eradication of smallpox arguably represents the greatest public health feat in the history of civilization.
In 1958, the Eleventh World Health Assembly (on the proposal of the USSR) approved a resolution for world-wide smallpox eradication under the auspices of World Health Organization (WHO). In that year alone the disease occurred in 59 countries, with many other areas experiencing imported cases.
During the next seven years progress was made in improving vaccine quality and safety, and a number of countries became free of smallpox; yet the disease continued to be widespread. When the intensified eradication programme began in 1967, there were 33 countries with endemic smallpox and two more countries subsequently became endemic.
The strategy of the eradication programme had two important goals: vaccination of at least 80% of the population and employment of adequate surveillance and containment systems. Between 1967 and 1971, WHO-supported national programmes were initiated in all endemic countries.
Global smallpox incidence began to decline rapidly, partly due to the provision of sufficient quantities of heat-stable vaccine of assured potency. The earliest successes occurred in a contiguous bloc of 21 western and central African countries, which became smallpox-free in merely three and a half years.
By the end of 1971, smallpox has been eliminated from all but three countries in eastern and southern Africa, and the eradication of the disease from Western Hemisphere was marked by the occurrence of Brazil's last cases in April 1971. Nevertheless, setbacks were confirmed as certain countries (such as Bangladesh) became reinfected.
Therefore in September 1973 intensified campaigns began in the five remaining endemic countries (Bangladesh, Ethiopia, Pakistan, India and Nepal). Ample resources and experienced staff were mobilized from many countries, and on 26 October 1977, the world's last outbreak was contained.
On May 8, 1980, the 33rd World Health Assembly declared the world free of smallpox. This followed approximately two and a half years after the last documented naturally occurring case of smallpox was diagnosed in a hospital worker in Merca, Somalia. At that time, all routine vaccination programs were terminated, given the success of this monumental eradication achievement.
Several factors facilitated the eradication effort. The highly accurate viral DNA polymerase minimized antigenic variation of variola virus and made vaccination effective everywhere; furthermore, acutely ill patients were the only source of infection (as a result of no animal reservoir), and the isolation was an effective control measure.
The ultimate expenditures of the intensified eradication program were approximately 23 million US dollars per year between 1967 and 1979, including 98 million US dollars from international contributions and 200 million US dollars from the endemic countries. The largest donor was the United States.
Despite plans to destroy all stocks of the virus by the end of the 20th century, they was never realized. Preservation of the virus is justified by the stated need (among others) to develop and evaluate antiviral agents, as variola virus represents a potential bio-weapon.