Polio Vaccine, and Cancer : Part 2

by CDC

(Page 2 of 3)

Were any other people in the United States possibly exposed to SV40-contaminated vaccines?

Yes. SV40 was a contaminant of respiratory syncytial virus given to a few volunteers in an experimental study of infection with the live virus. In addition, SV40 was also found in adenovirus vaccines given to more than 100,000 young men in army camps in the 1950s and 1960s to protect them from respiratory infections.

Is receiving contaminated vaccine the only way to become infected with SV40? Does it spread from person-to-person?

Receiving contaminated vaccine is not the only way to become infected with SV40. Data suggest that SV40 has infected a small percentage of the human population independently of the polio vaccine. A study of German medical students found that 12% had SV40 antibodies in 1952, before the introduction of the polio vaccine. Moreover, SV40 has been identified in people born in the 1980's and 1990's, well after the elimination of SV40 contamination from polio vaccines. This has led some to consider that the virus may spread from person-to-person. Some laboratory workers may have been exposed to SV40. It is not known whether people who live in countries with wild rhesus monkeys also could be exposed to SV40. Exactly how SV40 is transmitted among humans and how common it is among people in the U.S. population are unknown.

SV40 is known to cause tumors in rodents. Have research studies found an association between SV40 and cancer in humans?

Yes. An association has been found between SV40 and certain types of cancer in humans. However, though the virus or its DNA have been found in certain types of cancer, it has not been determined that SV40 causes these cancers. Finding that two events are "associated" is not the same as establishing that one event caused the other.

SV40 was linked with mesothelioma after tumors developed in hamsters that were injected with SV40 into the lungs, heart and abdomen. 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. In addition, reports have documented an association between SV40 and brain and bone tumors.

Two recent studies also found an association between SV40 and non-Hodgkin's lymphoma. These studies identified the virus in 42-43 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?

When SV40 was discovered in 1960, researchers did not know if the virus could negatively affect health. Many viruses that harm animals have no effect on people because of the biological differences between animals and humans. However, to investigate the possibility, several federally funded studies were carried out during the 1960s, 1970s and 1980s to follow persons who received polio vaccines (the results from some of these studies are discussed below). In addition, on January 27-28, 1997, the U.S. Food and Drug Administration, the Centers for Disease Control and Prevention, the National Institutes of Health, and the National Vaccine Program Office sponsored an open public meeting with scientists and physicians to discuss research findings on SV40. At the meeting they discussed available data and determined that further research into the field of SV40 was needed=.

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 affects of receiving SV40-contaminated vaccine? Has there been an increase in cancer among people who received SV40-contaminated polio vaccine?

The majority of evidence suggests there is no causal relationship between receipt of SV40-contaminated polio vaccine and cancer development; however, some research results in this area are conflicting and more studies are needed.

Since the discovery of SV40, several studies have been done to compare cancer rates in groups of individuals known or strongly presumed to have received SV40-contaminated polio vaccine to rates in persons known or strongly presumed not to have received SV40-contaminated vaccine. A brief description of some of these studies follows:

Two studies examined mesothelioma tissue from a small number of patients in Turkey, where SV40-contaminated vaccines were not used, and found no SV40. The researchers also examined mesothelioma tissue from a small number of patients in the US and Italy, where SV40-contaminated polio vaccines were used, and found SV40 in some of the specimens.

About the Author

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