NEWS

Vaccine’s History Prompts Years of Research

Nancy J. Nelson

The story began in 1960 when, shortly after its discovery, SV40 was detected in monkey kidney cells that were used in the production of the original Salk and Sabin polio vaccines. A year later, scientists showed that SV40 produced abnormalities in animal cells and caused cancer in hamsters. (SV40 typically does not cause symptoms or disease in any of the several species of monkeys it infects.)

Because of concerns about possible adverse effects on human health, the federal government instituted a screening program in 1961 requiring that all polio vaccines be free of the virus. No SV40 has been found in the polio vaccine lots tested in the United States after 1963, and the polio vaccine now used in the United States is produced under carefully regulated conditions designed to ensure that contamination with SV40 does not occur.

As a result of the earlier contamination, however, it is estimated that 10 million to 30 million people vaccinated in the United States from 1955 through early 1963 were inadvertently exposed to live SV40 virus. Most were immunized as young children, with the highest risk of exposure for people born from 1941 through 1961. Worldwide, hundreds of millions of people were exposed to SV40 through these contaminated vaccines.

The extent of the exposure precipitated four decades of intense research to determine whether the virus is linked to any human health problems, particularly cancer. Epidemiological reports have been reassuring. After decades of observations, large follow-up studies involving several million people in the United States and Europe have failed to detect an increased risk of cancer in those likely to have been exposed to the virus.



             
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