In July, 1961, Merck and Parke-Davis recalled their Salk vaccines — without mentioning the cancer risk. NIH officials concealed the SV40 cancer risk and never recalled the rest of the polio vaccine supply. Even after they knew that the vaccine was infected, they continued to expose millions of Americans to the serious risks of cancer for an additional two years. In total, 98 million Americans received contaminated vaccine shots from 1955–1963. [Debbie Bookchin and Jim Schumacher. The Virus and the Vaccine: …Contaminated Polio Vaccine, and the Millions of Americans Exposed, 2004]