According to The River, a book written by Edward Hooper, the most likely source of AIDS in humans can be traced to the Dr. Koprowski strain of oral polio vaccine used during the polio eradication trials conducted in the Belgian Congo during the 1950s. Since Dr. Koprowski used monkey kidney tissue as a substrate in which to grow and attenuate the polio virus prior to it's being administered to humans, and since a some of the monkey kidney substrate would have contained HIV/AIDS viruses, it is highly probable that the HIV/AIDS virus carried by monkeys was introduced to the human species by contaminated oral poliovacines.