When HIV first became prominent as a mysterious disease, people had many theories of how it was spread, almost all of them focused on the “immoral and drug-fueled” sexual activities of highly stigmatized groups. They not only held very strong views but they were absolutely certain that they were right. But the public, politicians and scientists were all challenged to rethink their ideas of spread when confronted by reports that the disease could be transmitted by infusing clotting factors from a donor to a patient with hemophilia.

An effective vaccine for preventing smallpox had been discovered and tested by 1796. And by the 1970’s widespread vaccination resulted in most people in rich countries being vaccinated and almost completely protected. Smallpox was actually eliminated from developed countries in the 1970s. But the burden of smallpox was inequitably distributed. People in some poor countries remained vulnerable and faced high risks of mortality from smallpox. It was within the poorest communities that smallpox was spread.