Second, when Alex says that they put SV40 in polio vaccines, he's lying. Between 1955 and 1963, approximately 10-30% of polio vaccines were contaminated with what's known as SV40, or simian virus 40. The reason for this was that at the time, vaccines were made using monkey kidney cell cultures, and unbeknownst to the vaccine makers, some of the vaccines were contaminated. Obviously, that's not good. However, according to the CDC, quote, there has been some concern that the virus could cause cancer in humans. However, most studies looking at the relationship between SV40 and cancers are reassuring, finding no causal association between the receipt of SV40 contaminated polio vaccine and the development of cancer.