Study Is Unsure on Tainted Polio Vaccine's Cancer Role

By DENISE GRADY

he polio vaccine used in the United States from 1955 to 1963 has long been known to have been contaminated with a cancer-causing monkey virus, but even after years of study it is not clear whether the vaccine is linked to any cancers in people, scientists reported yesterday.

Still, if the vaccine does contribute to cancer, it is highly unlikely to cause more than an extremely small increase in the risk for certain rare types, the scientists say.

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The possibility of a cancer connection has worried some researchers because the vaccine, made in monkey cells, was found in 1960 to be contaminated with a monkey virus called simian virus 40, or SV40. The tainted vaccine was never recalled. It may have been given to 10 million to 30 million Americans, researchers say. Vaccines made after 1961 were free of the virus.

SV40 can cause cancer in rodents and in cultured human cells. It has been found in some tumors taken from cancer patients.

But finding the virus in a tumor does not prove that it caused the tumor. Most large population studies have not found a higher cancer risk in people exposed to the vaccine. There is no blood test that can tell whether a person is infected with SV40, and there are no special steps to take to prevent the rare cancers being studied, researchers said.

The report released yesterday was prepared by a 14-member committee on vaccine safety convened by the Institute of Medicine, which advises the government on public health. The report is the fifth in a series of eight that the government commissioned on vaccination. Fear of vaccine side effects has led some parents to shun vaccination, and outbreaks of diseases like whooping cough and measles have resulted, the report said.

After analyzing more than 100 studies, the committee said that most evidence argued against a connection between the polio vaccine and cancers, but that those weaknesses in the studies made it impossible to dismiss the potential link.

There is no doubt that SV40 causes tumors in rodents. Four cancers have been linked to it in animals, the bone tumors called osteosarcomas; ependymoma, a type of brain tumor; mesothelioma, a cancer in the membranes around lungs and other organs; and non-Hodgkin's lymphoma, a cancer that affects the immune system. But it is not clear whether the virus causes tumors in people.

The virus has been detected in tumor cells from people with the four cancers that develop in rodents. Whether it caused the tumors is not known, nor is it known whether people with the virus contracted it from polio vaccine or whether the virus can spread between people. The virus may have been in other vaccines. SV40 may also spread from animals to people who work with them and to laboratory workers.

Because certain information is missing, the question of whether the vaccine ever caused cancer in a human being may never be fully resolved, said Dr. Steven Goodman, a committee member and an expert in cancer and statistics from the Johns Hopkins School of Medicine.

Researchers do not know how much of the vaccine was contaminated or which vaccine was given to which people. Study subjects were assumed to have received either tainted or virus-free vaccine solely on the basis of their birth dates.

Dr. Marie McCormick, chairwoman of the vaccine panel and chairwoman of the Department of Maternal and Child Health at the Harvard School of Public Health, said samples of the old vaccine lots were not saved, so no tests can be conducted to measure the extent of the contamination or to determine who received what.

Dr. McCormick said there were lessons to be learned from the contamination. She noted that there was still no long-term storage of samples that could be checked in case a question of contamination or other problem arose later.

"One consideration might be to store lots," she said. "The companies have no obligation to keep them beyond the expiration date."

She said it might also be worthwhile to develop better ways to track who received which lots and of notifying health officials, doctors and patients if contamination was detected.

Vaccine companies have been the target of suits.