VACCINES

Monkey Virus in Polio Vaccine

The ability to culture the polio virus in cells was the breakthrough that permitted the mass production of the polio vaccine in the 1950s. Either human or animal cells can be used. Salk vaccine manufacturers used Rhesus monkey kidney cells, a choice that was expedient, but may prove to have been a costly mistake. In 1961, a monkey virus called SV40, that appears to disable anticancer defenses, was detected in the vaccine.

By the time the contamination was discovered, the vaccine had already been administered to nearly 100 million Americans and to unknown numbers elsewhere. The federal government ordered manufacturers to find a monkey species that did not carry SV40, and the switch was made to African green monkeys. The problem was not announced to the public, however, and the government permitted the older, contaminated vaccine batches to be used until 1963.

In 1994, researchers discovered the virus in patients with a form of cancer called mesothelioma, which is diagnosed in 2,000 to 3,000 Americans each year. While this unusual form of lung cancer is normally linked to asbestos exposure, between 20 and 50 percent of cases have no such history. The virus has also cropped up in other cancers, including those of the brain and bone. Researchers suspect that the vaccine, tainted by monkey viruses, may have contributed to these cancers. African green monkeys carry viruses of their own, including immunodeficiency viruses, raising speculations as to the role of vaccinations in AIDS. Great Britain and Canada already mandate the use of cloned human cells, rather than animal cells, for vaccine production. While this method is more expensive than using animal cells, it is difficult to avoid the conclusion that the U.S. should follow suit.

CHILD HEALTH

Fish and Mental Deficits

Health and politics are clashing again, as Michigan governor John Engler refused to issue warnings to women and children about the risks of polychlorinated biphenyls (PCBs) in Great Lakes fish. Although the Environmental Protection Agency had agreed with Great Lakes states to issue warnings about the fish in order to avoid damage to the developing brains of babies and children, Engler refused to issue the warnings in his state. Salmon are stocked in the waters as a boon to the Michigan recreation industry.

Great Lakes salmon, like many other fish species, are heavily contaminated with PCBs—industrial chemicals that have long been associated with brain disorders in children. Studies in the 1980s showed that women consuming Lake Michigan fish just two to three times per month were more likely to have children who were sluggish at birth, had a small head circumference, or showed cognitive difficulties. A September 1996, New England Journal of Medicine study found lower intelligence and achievement test scores in 11-year-old children whose mothers had consumed Lake Michigan fish during pregnancy and suggested that PCBs were the cause.

CANCER

Exercise Cuts Cancer Risk

Women who exercise regularly have one-third less risk of breast cancer compared to sedentary women, according to a study published in the New England Journal of Medicine. By following 25,624 women in Norway over a 14-year period, researchers found that those who engaged in walking or bicycling at least four hours or more per week had one-third less risk. Higher levels of exercise reduced risk even further.

Exercise affects many aspects of physiology. The reduction in cancer risk may relate to the fact that vigorous physical activity reduces the amount of estrogen the body produces. In extreme cases, it can even suppress ovulation. Women with less estrogen in their blood generally have less risk of breast cancer.

Thune I, Brenn T, Lund E, Gaard M. Physical activity and the risk of breast cancer. N Engl J Med 1997;336:1269-75.