How the Simian virus got into the Polio vaccine is a story and a half.

Dr Mary's Monkey

Dr. Mary’s Monkey: How the Unsolved Murder of a Doctor, a Secret Laboratory in New Orleans and Cancer-Causing Monkey Viruses are Linked to Lee Harvey Oswald, the JFK Assassination and Emerging Global Epidemics.

The 1964 murder of a nationally known cancer researcher sets the stage for this gripping exposé of medical professionals enmeshed in covert government operations over the course of three decades. Following a trail of police records, FBI files, cancer statistics, and medical journals, this revealing book presents evidence of a web of medical secret-keeping that began with the handling of evidence in the JFK assassination and continued apace, sweeping doctors into coverups of cancer outbreaks, contaminated polio vaccine, the arrival of the AIDS virus, and biological weapon research using infected monkeys.

https://www.goodreads.com/book/show/10255.Dr_Mary_s_Monkey