Frequently Asked Questions about Cancer, Simian Virus 40 (SV40), and Polio Vaccine
SV40 is a virus found in some species of monkey. Soon after its discovery in 1960, SV40 was found in polio vaccine. More than 98 million Americans received one or more doses of polio vaccine during the period (1955–1963) when some of the vaccine was contaminated with SV40. SV40 has been found in certain types of human cancers, but it has not been determined that SV40 causes these cancers. The majority of evidence suggests there is no causal relationship between receipt of SV40-contaminated vaccine and cancer; however, some research results are conflicting and more studies are needed. For more information, see the fact sheet.
What is SV40?
SV40 is not related to HIV, the virus that causes AIDS in humans, or to simian immunodeficiency virus (SIV), the virus that causes an AIDS-like disease in some monkey species.
Why is there so much interest in SV40?
Interest in SV40 has increased in the last several years because the virus was found in certain forms of cancer in humans, for instance mesotheliomas (rare tumors located in the lungs), brain, and bone tumors (Carbone et al., 1994; Jasani et al., 2001). More recently, SV40 has also been found to be associated with some types of non-Hodgkin’s lymphoma (Shivapurkar et al., 2002; Vilchez et al., 2002).
SV40 was completely removed from the seed strains of the vaccine viruses in the early 1960s.The polio vaccine currently used in the U.S. (inactivated polio vaccine, or IPV) is no longer prepared in primary rhesus monkey kidney cells. It is produced in human or African green monkey cell lines that have been extensively tested for contaminants, including SV40.The poliovirus used in IPV is killed with formaldehyde. This procedure also kills viral contaminants, such as SV40. Formaldehyde was also used in the SV40-contaminated vaccine, but in 1961 researchers found that the process killed 99.99% of SV40 and 1 in 10,000 SV40 particles survived (Hilleman, 1998).Today’s testing methods are better. Any live SV40 would be detected by these methods.
What about concerns that the testing methods used to screen oral polio vaccines could have missed certain strains of SV40?
A study (Rizzo et al., 1999) raised concern that some lots of OPV may have been contaminated with a slow-growing SV40 strain that would not have been detected with the methods used to test it. However, this study did not follow the actual testing protocol used to ensure that vaccine is free of SV40. Subsequent studies (Minor et al., 2001) confirmed studies from the early 1960s (Melnick) showing that the testing methods used were sufficient to detect even slower-growing strains of SV40. In addition, researchers from the FDA used the very sensitive polymerase chain reaction (PCR) methodology to search for SV40 DNA in OPV manufactured in the U.S. between 1972 and 1996 (the FDA only tested vaccines produced as far back as 1972, because there were no existing lots of OPV at FDA that were produced between 1962 and 1972). SV40 DNA sequences were not found in any of the vaccine lots tested (Sierra Honigmann & Krause, 2000). OPV is no longer produced in the U.S.; if production were to be resumed, it would continue to be under extremely strict conditions that eliminate the possibility of any contamination with SV40.
Who received SV40-contaminated polio vaccine in the U.S.?
Were any other people in the United States possibly exposed to SV40-contaminated vaccines?
Is receiving contaminated vaccine the only way to become infected with SV40?
SV40 is known to cause tumors in rodents. Have research studies found an association between SV40 and cancer in humans?
SV40 was linked with mesothelioma after tumors developed in hamsters that were injected with SV40 into the lungs, heart and abdomen (Cicala et al., 1993). Mesotheliomas are rare cancers usually located in the lining of the lungs in humans and are associated with asbestos exposure. SV40 has been found in 47% to 83% of human mesothelioma tumors (Carbone, 1999). In addition, reports have documented an association between SV40 and brain and bone tumors (Jasani, 2001).
Two recent studies also found an association between SV40 and non-Hodgkin’s lymphoma (Shivapurkar et al., 2002; Vilchez et al., 2002). These studies identified the virus in 42 to 43 percent of non-Hodgkin’s tumors, while finding no SV40 in tissue from healthy study volunteers. Lymphoma is a general word for cancers that develop in the lymphatic system – the tissues and organs that produce, store and carry white blood cells that fight infection and other diseases. Hodgkin’s disease is one type of lymphoma; all others are called non-Hodgkin’s lymphoma. Lymphomas account for about 5 percent of all cases of cancer in this country.
What steps have been taken by the government to see if SV40-contaminated vaccines affected people’s health?
In 2001, the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) asked the National Academy of Sciences’ Institute of Medicine (IOM) to establish an independent expert committee to review hypotheses about existing and emerging immunization safety concerns. These reviews involve an assessment of factors such as the biologic mechanisms of the hypothesis, alternative hypotheses, as well as the available scientific evidence to date. In 2002, the IOM Immunization Safety Review Committee examined the existing scientific data on SV40-contaminated polio vaccine and cancer. The committee did not recommend* review of the current polio vaccine recommendations on the basis of concerns about cancer risks, because the vaccine in current use is free of SV40. However, the committee recommended development of sensitive and specific blood tests for SV40 and techniques for SV40 detection. When this has been done, the committee recommends that pre-1955 samples of human tissue be tested for SV40. They also recommended further study into how SV40 may spread among humans, and argued that additional studies of people who may have received contaminated vaccine should not be done until technical (laboratory) issues are resolved.
What has research found regarding the health effects of receiving SV40-contaminated vaccine?
In summary, the majority of studies in the U.S. and Europe that compare persons known or strongly presumed to have received SV40-contaminated polio vaccine with those known or strongly presumed not to have received SV40-contaminated polio vaccine have not shown a causal relationship between receipt of SV40-contaminated polio vaccine and cancer. It should be noted, however, that SV40 infection has been found in persons who did not receive SV40-contaminated polio vaccine and that for some study participants it cannot be known with certainty whether or not they received SV40-contaminated vaccine. Because of this, there may be errors in these studies that make it harder to detect a true increased cancer risk associated with receipt of SV40-contaminated polio vaccine. In addition, research is needed that focuses on the long-term consequences of SV40 exposure, as some cancers like mesotheliomas typically occur later in life and would not have been detected in several of the studies described above. Moreover, additional studies are needed which focus on the potential long-term effect of SV40 exposure on health outcomes other than cancer (Strickler and Goedert, 1998). Because the CDC takes this issue very seriously, the agency has asked an expert committee to review the existing data on this topic and provide recommendations for future research.
Have research studies looked at the risk of cancer in children whose mothers received SV40-contaminated polio vaccine?
Additional studies are needed that focus on maternal vaccination with SV40-contaminated vaccines and risk of cancer and other health effects in offspring.
Can I obtain a test to see if I am infected with SV40?
What should I do if I received polio vaccine during 1955–1963?
Where can I get more information about SV40?
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Page last modified: October 22, 2007
Content source: Immunization Safety Office