Simian Virus 40 (SV40) was discovered in 1960 in rhesus monkey kidney cells used to produce both the Salk inactivated polio vaccine and early Sabin oral polio vaccine. An estimated 10-30 million Americans and up to 100 million people globally received SV40-contaminated polio vaccines between 1955 and 1963. NIH virologist Bernice Eddy detected the contamination in 1960 but stockpiles continued to be used. SV40 causes sarcomas in hamsters and was subsequently detected in human tumours. The IOM 2002 review concluded the biological mechanism was plausible but epidemiologic data were inconclusive. Contamination is documented fact; cancer causation in humans remains contested.