Smallpox one-third of the cases resulted in blindness. These deaths included those of four reigning monarchs and a queen consort. In the 20th century smallpox killed 200-300 million people. Edward Jenner discovered in 1798 that vaccination could prevent smallpox. 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 15th century to distinguish the disease from syphilis, which was then known as the "great pox". Other historical names for the disease include pox, speckled
Vaccination policy once vaccination rates reach a certain level, even if this level is below that optimal for the community. For example, a 2003 study found that a bioterrorist attack using smallpox would result in conditions where voluntary vaccination would be unlikely to reach the optimum level for the U.S. as a whole, and a 2007 study found that severe influenza epidemics cannot be prevented by voluntary vaccination without offering certain incentives. Governments often allow exemptions to mandatory vaccinations for religious or philosophical reasons, but decreased rates of vaccination may cause loss of herd immunity, substantially increasing risks even to vaccinated individuals.