During the 1950s, the inactivated polio vaccine created by Jonas Salk was made using rhesus monkeys that were infected with SV40, a monkey virus that was later linked to cancer in humans.
From 1955 to 1963, hundreds of millions of people worldwide in North and South America, Canada, Europe, Asia and Africa received the vaccines, which at the time were heralded as a medical breakthrough.
In the archived 1956 video below, you can see a propaganda piece from that era, showing just how the ill-fated vaccine was made.
Few back then grasped that these vaccines might also be a huge, inadvertent, uncontrolled experiment in interspecies viral transmission, a 2004 article in The Lancet noted.
SIV 40(Simian Immunodeficiency Virus 40) was the 40th Simian virus found in the polio vaccine. It caused a surge of lung disease even in people who never smoked.