WHO

Disease Eradication/Elimination Goals
In 1967, the WHO began a campaign to eradicate smallpox. This was an enormous and complex exercise which involved the systematic vaccination of entire populations in endemic countries. By 1972, the incidence of the disease had fallen rapidly, with cases occurring in only eight of the endemic countries in Africa and southern Asia. In 1980, the World Health Assembly declared the global eradication of the disease.

Smallpox no longer affects anyone and the cost of getting rid of it - approximately $313 million over 10 years - has been repaid many times in saving of human lives and in the elimination of costs for vaccines, treatment and international surveillance activities.

Today, WHO stands poised to eradicate or eliminate as a public health problems six other diseases or disorders by the year 2000.

Definitions:
Control of disease, when applied to many communicable and some noncommunicable conditions, is defined as ongoing operations or programmes aimed at reducing the incidence and/or prevalence, or eliminating such conditions.
Elimination of disease is defined as the reduction of case transmission to a predetermined very low level; e.g., elimination of tuberculosis as a public health problem was defined by WHO in 1991 as a reduction of prevalence to a level below one case per million population.
Eradication of disease is defined as achievement of a status whereby no further cases of a disease occur anywhere, and continued control measures are unnecessary (see smallpox example above).

Source: http://www.who.int/aboutwho/en/disease_er.htm