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.
Countdown to Extinction some of the biggest hooks the genre had ever seen". In a retrospective review of the album, Craig Hayes from Popmatters wrote that "Countdown to Extinction"'s "status as a gateway metal album is indisputable" and its "popularity speaks volumes about its significance in the metal canon". The group started the "Countdown to Extinction" tour in 1992 with Pantera, Suicidal Tendencies and White Zombie as the opening acts. They headlined the Roskilde Festival in Copenhagen on June 27 the same year, and continued with dates in Europe during the summer. The tour carried on throughout 1993, with the band making appearances