Current Status of Research on Simian Virus 40

National Cancer Institute
Tuesday, 2 March 1999

Current Status of Research on Simian Virus 40

SV40 is a simian virus that infects several species of monkeys. The virus first gained widespread attention in 1960 when researchers found that SV40 was one of many of viruses that contaminated kidney cells from rhesus macaque monkeys that were used in the production of the original Salk and Sabin polio vaccines.

Concerns about possible adverse health effects of SV40 soon surfaced when scientists showed that it produced abnormalities in animal cells and caused cancer in hamsters. Based on these and other studies, the federal government in 1961 required that the polio vaccine must be free of the virus, although it is likely that some SV40-tainted vaccines might have been administered in some areas of the United States as late as 1963.

Over the next two decades, an intense research effort ensued to determine whether SV40 also caused cancer in people. The largest studies ultimately showed no increase in cancer or cancer-related death among people who were given the SV40-contaminated polio vaccine. However, some smaller studies suggested a increased risk of certain rare cancers in people who were exposed to the early vaccines.

The issue of SV40-tainted polio vaccines resurfaced recently when scientists using the powerful techniques of molecular biology, specifically polymerase chain reaction or PCR, found traces of the virus in some rare human tumors including mesothelioma, (a cancer of tissues that line organs, such as the lung); osteosarcoma, (a type of bone cancer) and ependyoma (a type of brain tumor). But again, the association between SV40 and cancer remained uncertain when other scientists failed to detect SV40 in the tumors.

Currently, the issue remains unclear. But, there is a large and growing body of data indicating that exposure to the tainted polio vaccines has not led to an outbreak in the United States of mesotheliomas, osteosarcomas, or ependyomas. In January 1997, scientists at the National Cancer Institute (NCI) reported that after more than 30 years of follow-up, a large group of Americans exposed to the early SV40-contaminated polio vaccines have not had an increased rate of these cancers. They are rare and continue to be rare in the United States.

The lone exception is mesothelioma, which has increased in the United States and is related primarily to asbestos exposure through the 1970s. However, a similar increase in mesotheliomas also has been found in Sweden, a nation that largely was not exposed to SV40-contaminated polio vaccines. This suggest that the rates for these cancers may be on the rise in many countries due to factors unrelated to SV40 exposure.

The NCI also has nearly completed a large international collaborative study to resolve why some laboratories detect traces of SV40 in mesothelioma, while others do not. The results are expected to be published by the end of the year.

For more information, or to contact National Cancer Institute, see their website at: www.cancer.gov