The WHO Eradication Programme
Today it is often difficult to imagine that smallpox was once one of the most feared diseases in ancient and modern history. In 1956, the World Health Organization (WHO) began a first programme to eradicate smallpox by vaccination. The nature of smallpox infection made this a difficult undertaking for the following reasons:
1. Duration of immunity: Smallpox vaccination does not grant lifelong immunity to the disease; in fact, immunity lasts an average of 5-7 years. Individual immunity, however, varies greatly - from 4 months to more than 10 years. As a result, vaccination campaigns had to incorporate significant revaccination efforts.
2. Subclinical cases: If a vaccinated person has some existing, but diminishing immunity against smallpox, the disease can still be contracted in milder, less recognizable forms. Since key symptoms like fever and rash were mostly absent in such persons, transmission of the disease by undiagnosed vaccinated persons was a frequent occurrence.
Mainly for these reasons, the first attempt to eradicate smallpox was unsuccessful. In the late 1960s, the WHO modified their strategy to incorporate two critical components: a mass vaccination campaign in each country involved, and the implementation of a system that contained outbreaks by vaccinating close contacts of index smallpox cases.
This new approach, called the Global Intensified Eradication Programme (1967-1977), proved to be more effective. The drop in the number of cases was particularly dramatic in India, the country with the highest smallpox morbidity, which experienced 27.407 cases in 1972; 87.240 cases in 1973; 188.003 cases in 1974; but only 1.436 cases in 1975. In 1976, the only cases of smallpox were isolated cases in Ethiopia. The last recorded naturally occurring case of smallpox happened in Somalia in 1977, and on May 8, 1980, the WHO declared the global eradication of smallpox. There has not been a single reported case of smallpox infection in over twenty years.