“The concern scientists had regarding passenger viruses was not unfounded. You may recall the disastrous SV40 monkey virus which contaminated the polio vaccines. There are scientists who claim this virus is the cause of multiple human cancers. On CDC’s website a page on vaccine safety, which was suddenly removed (archived copies exist), states that: “SV40 virus has been found in certain types of cancer in humans, but it has not been determined that SV40 causes these cancers.”