Immunization is the best way to protect people from a host of diseases. But 40 years ago, it was discovered that a polio vaccine given to millions of people was contaminated with a virus that experts say could cause cancer. A new study concludes the risk to people who were vaccinated appears slight.
Between 1955 until 1963, experts estimate as many as 98 million people in the United States received the oral polio vaccine. Millions more received the drug in United Kingdom, Australia, Germany, and Sweden.
The concern is that the vaccine during those years was grown in a culture that contained cells of the rhesus monkey, which may have been infected with a virus known as Simian virus 40. The virus is harmless to monkeys, but animal studies in the 1990's have shown that it can cause a variety of cancers, including cancers of the lung, bone, and lymphatic system.
After 1963, people were vaccinated against polio with a drug that did not use rhesus kidney cells. But public worry sparked a study on whether there is an increased cancer risk to people who received the old vaccine.
Marie McCormick heads the Department of Maternal and Child Health at Harvard School of Public Health in Cambridge, Massachusetts.
Dr. McCormick chaired the study by a committee of the (U.S.) National Academy of Sciences looking at a possible link between the oral polio vaccine and cancer. According to Dr. McCormick, the majority of population-based studies..." have found no increase in the rates of cancer in the people during the period of contamination," said Marie McCormick.
But Dr. McCormick cautions it is impossible for researchers to know who received contaminated vaccine decades ago. So, their conclusion is not iron clad. Dr. McCormick notes cancers that may be associated with the old oral polio vaccine are extremely rare in the population, with only a relatively few new cases diagnosed every year.
Dr. McCormick believes people who received the vaccine between 1955 and 1963 should not be too concerned. "Being one of those people, I remember the restrictions on my life due to the threat of polio, and the summer epidemics that occurred," she said. "So, I think one of the take home messages is that we have been protected against a very serious disease."