The poliovirus vaccine that was used in mass immunization programs in the late 1950s and early 1960s had been contaminated with the monkey virus SV40, or simian virus 40. The virus has been shown to cause tumors in mice when injected in high amounts. It has also been detected in some human tumors, particularly pleural mesothelioma, which is a rare cancer of the membrane that covers the lungs.
When rates of pleural mesothelioma increased between 1975 and 1997, suspicion of a link to the vaccine was raised.
But research published in the Jan. 1 issue of Journal of the National Cancer Institute shows that trends in the cases of mesothelioma were not consistent with exposure to SV40-contaminated poliovirus vaccine.
Using cancer data from the National Cancer Institute's Surveillance, Epidemiology and End Results Program, researchers with the Albert Einstein College of Medicine in New York City analyzed age- and sex-specific rates of pleural mesothelioma from 1975 through 1997, and compared the data with information on exposure to the SV40-contaminated poliovirus vaccine.
The researchers found that the rise in pleural mesothelioma cases was mostly among males who were 75 or older -- the age group that was least likely to have been exposed to the contaminated vaccine. Cases of the cancer among males in the age group that had been exposed to the vaccine remained either stable or decreased. The patterns among females were similar.
The researchers say the fact that no link between the contaminated vaccine and cancer has been found in almost 40 years of follow-up is promising, but they add that observation of people exposed to the vaccine should continue, because of the link between SV40 and some tumors.
Here's more information about vaccine safety from the Centers for Disease Control and Prevention.