During the 20th century, it is estimated that smallpox was responsible for 300–500 million deaths.[7][8] As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that two million died in that year.[9] After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in 1979.[9] To this day, smallpox is the only human infectious disease to have been completely eradicated from nature.[10]