BETHESDA, MARYLAND - Recent reports that the DNA of a virus called SV40 monkey is hiding in some rare types of human cancers has revived a controversy nearly 40 years on the safety of a vaccine against polio was widely administered to the late 1950. But at the end of a symposium held yesterday and today at the National Institutes of Health (NIH) to vet new evidence, many experts have emerged convinced that the virus does not pose a threat to people.
The dispute originally erupted in 1960 when researchers discovered that some batches of vaccine against polio, which was made from killed whole virus grown in monkey cells was infected with SV40. The discovery raised the alarm bells a year later, when it was found that SV40 injected into hamsters can trigger cancerous tumors. The controversy died down after studies of the human population has failed to establish evidence of increased rates of cancer among vaccinated individuals, and similar contamination problems are not likely to occur now because the cells used to grow viruses for vaccines are screened to remove any SV40 bearing.
in 1994, however, the researchers found the DNA of SV40 in mesothelioma, a rare tumor associated with exposure to asbestos, and a pair of studies published in the last month reports having found viral DNA in several types of brain tumors, and osteosarcoma, a type of bone tumor. This suggests that the infection could lead to cancer, as it does in animals. Other laboratories have not been able to duplicate some of the studies of the tumor, however, NIH and called the meeting to analyze all the data and try to reach consensus on what observations could mean viral.
So far, the researchers agree, there is no reason to doubt the original reports. "It seems that there is probably something there," says virologist Michael Fried Imperial Cancer Research Fund in London. But as before, the tone prevailing at the conference was that SV40 does not seem to pose a threat. In a just completed study, Swedish and American epidemiologists today announced that they have failed to document any increase in cancer in the generation of people who received contaminated vaccines. Concludes Arthur Levine, a co-organizer of the symposium and virologist National Institute of child health and human development, "There is no evidence that the apparent damage occurred as a result of this massive exposure to SV40." The next step, experts say, will further explore why shows SV40 in these tumors in the first place.
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