Final answer:
Smallpox was eradicated due to the development of the vaccine by Edward Jenner, and an intensive global vaccination campaign led by the WHO, targeting all endemic areas. By 1977, the virus was no longer naturally occurring, and smallpox was officially declared eradicated in 1980 because it is a disease with humans as its only reservoir.
Step-by-step explanation:
How Smallpox Was Eradicated
The eradication of smallpox stands as a monumental achievement in public health. Prior to its eradication, smallpox had a catastrophic impact on populations across the world, including Native American communities who had no immunity to the disease upon first contact with Europeans. The basis for the smallpox vaccine originated from the practice of inoculation, known as variolation, which existed as early as the 10th century in China. It was Edward Jenner's development of the vaccine through the use of cowpox material in the late 18th century that set the stage for modern vaccination against smallpox. Over centuries, the vaccine was perfected, making it safer and more effective.
In the 20th century, despite the existence of an effective vaccine, smallpox persisted, especially in unvaccinated populations. The World Health Organization (WHO) launched a mass vaccination campaign in 1959, intensifying their efforts with the Intensified Eradication Program in 1967. This global initiative targeted all areas where smallpox was still endemic. By the 1970s, the campaign had successfully eradicated smallpox in South America, Asia, and Africa. In 1977, the last natural case was recorded, and in 1980, the WHO declared smallpox eradicated globally - the only human infectious disease to have met this fate so far. This feat was made possible because humans are the only reservoir for smallpox, meaning that vaccination could effectively disrupt the disease's transmission cycle.