Smallpox was an infectious disease caused by one of two virus variants, Variola major and Variola minor. The agent of variola virus (VARV) belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) certified the global eradication of the disease in 1980, making it the only human disease to be eradicated.The initial symptoms of the disease included fever and vomiting. This was followed by formation of ulcers in the mouth and a skin rash. Over a number of days, the skin rash turned into the characteristic fluid-filled blisters with a dent in the center. The bumps then scabbed over and fell off, leaving scars. The disease was spread between people or via contaminated objects. Prevention was achieved mainly through the smallpox vaccine. Once the disease had developed, certain antiviral medication may have helped. The risk of death was about 30%, with higher rates among babies. Often, those who survived had extensive scarring of their skin, and some were left blind.The origin of smallpox is unknown; however, the earliest evidence of the disease dates to the 3rd century BCE in Egyptian mummies. The disease historically occurred in outbreaks. In 18th-century Europe, it is estimated that 400,000 people died from the disease per year, and that one-third of all cases of blindness were due to smallpox. Smallpox is estimated to have killed up to 300 million people in the 20th century and around 500 million people in the last 100 years of its existence. Earlier deaths included six European monarchs. As recently as 1967, 15 million cases occurred a year.Inoculation for smallpox appears to have started in China around the 1500s. Europe adopted this practice from Asia in the first half of the 18th century. In 1796, Edward Jenner introduced the modern smallpox vaccine. In 1967, the WHO intensified efforts to eliminate the disease. Smallpox is one of two infectious diseases to have been eradicated, the other being rinderpest in 2011. The term "smallpox" was first used in Britain in the early 16th century to distinguish the disease from syphilis, which was then known as the "great pox". Other historical names for the disease include pox, speckled monster, and red plague.

The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of health". Headquartered in Geneva, Switzerland, it has six regional offices and 150 field offices worldwide.

The WHO was established on 7 April 1948. The first meeting of the World Health Assembly (WHA), the agency's governing body, took place on 24 July of that year. The WHO incorporated the assets, personnel, and duties of the League of Nations' Health Organization and the Office International d'Hygiène Publique, including the International Classification of Diseases (ICD). Its work began in earnest in 1951 after a significant infusion of financial and technical resources.The WHO's mandate seeks and includes: working worldwide to promote health, keeping the world safe, and serve the vulnerable. It advocates that a billion more people should have: universal health care coverage, engagement with the monitoring of public health risks, coordinating responses to health emergencies, and promoting health and well-being. It provides technical assistance to countries, sets international health standards, and collects data on global health issues. A publication, the World Health Report, provides assessments of worldwide health topics. The WHO also serves as a forum for discussions of health issues.The WHO has played a leading role in several public health achievements, most notably the eradication of smallpox, the near-eradication of polio, and the development of an Ebola vaccine. Its current priorities include communicable diseases, particularly HIV/AIDS, Ebola, COVID-19, malaria and tuberculosis; non-communicable diseases such as heart disease and cancer; healthy diet, nutrition, and food security; occupational health; and substance abuse. Its World Health Assembly, the agency's decision-making body, elects and advises an executive board made up of 34 health specialists. It selects the director-general, sets goals and priorities, and approves the budget and activities. The director-general is Tedros Adhanom Ghebreyesus of Ethiopia.The WHO relies on contributions from member states (both assessed and voluntary) and private donors for funding. Its total approved budget for 2020–2021 is over $7.2 billion, of which the majority comes from voluntary contributions from member states. Contributions are assessed by a formula that includes GDP per capita. Among the largest contributors were Germany (which contributed 12.18% of the budget), the Bill & Melinda Gates Foundation (11.65%), and the United States (7.85%).Since the late 20th century, the rise of new actors engaged in global health such as the World Bank, the Bill and Melinda Gates Foundation, the US President's Emergency Plan for AIDS Relief (PEPFAR) and dozens of public-private partnerships for global health have weakened the WHO’s role as a coordinator and policy leader in the field.