Pandemic smallpox was responsible for 300–500 million deaths. As recently as the early 1950s, an estimated 50 million cases of smallpox occurred in the world each year. After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in December 1979. To this day, smallpox is the only human infectious disease to have been completely eradicated, and one of two infectious viruses ever to be eradicated. Historically, measles was prevalent throughout the world, as it is highly contagious. According to the U.S. National Immunization Program, 90% of people were infected with measles by age 15.
Driven to refusal not budge the rod or pile. Driven to refusal This is an engineering term for describing how far to drive piles. It is also used in surveying when driving metal posts and monuments that are to be used as bench marks (ie. the elevation of which will be established to a high degree of accuracy). When a very high degree of stability is required the post will be inside an oil filled outer casing to protect it against movement of the surrounding ground usually because of the frost. A rod or pile has been "driven to refusal" when five more