Simian virus 40 (SV40) occurs commonly in rhesus monkey-kidney tissue used for propagating poliovirus, and is not entirely inactivated by formalin. Since this simian agent fails to cause obvious cytopathic effects in rhesus-kidney culture, it escaped detection and was incorporated in certain batches of formalinized vaccine used in the early years of polio immunization. The virus is now carefully excluded in the production of all virus seed stocks and vaccines of monkey-kidney origin. However, there has been concern that SV40 may be oncogenic for man, since it induces malignant tumors in young laboratory rodents and causes transformations suggestive of neoplasia in human tissue cultures.
In this issue of The Journal (p 713) Fraumeni, Ederer, and Miller, of the National Cancer Institute ( NCI ), present an analysis of cancer mortality rates among children during the 4 years after initiation of mass immunization with Salk vaccine. For its report, the NCI group took