Exposure to PCBs may reduce the effectiveness of vaccines in children.

New epidemiological evidence suggests that exposure to environmental pollutants may have an adverse impact on immune responses to childhood vaccinations. A report on the research appeared in the August 22, 2006, online edition of Public Library of Science Medicine.

The study looked at two groups of children in the Faroe Islands, which are located in the North Atlantic and where traditional diets may include whale blubber contaminated with polychlorinated biphenyls (PCBs). Blood and milk samples taken during pregnancy from the mothers were analyzed to determine the children's prenatal PCB exposure. After routine childhood vaccinations against tetanus and diphtheria, the two groups of children were examined at 18 months and seven years of age, and blood samples were examined for tetanus and diphtheria antibodies.

The findings showed an association between increased PCB contamination and lowered antibody response to the vaccines. At 18 months, the diphtheria antibody concentration decreased by 24 percent with each doubling of PCB exposure. At seven years, the tetanus antibody response showed the strongest response, decreasing by 16 percent with each doubling of prenatal exposure.

"Our study raises concern that exposure to PCBs and similar compounds may make childhood vaccinations less efficient," said Philippe Grandjean, adjunct professor at the Harvard School of Public Health and co-author of the paper. Exposed children may also be more susceptible to infections in general, he said.

The study had some limitations, including the relatively small numbers of children who were examined and the time intervals between collection of blood samples. PCBs are present in fatty fish worldwide and are known from laboratory studies to affect the development of the immune system. Evidence that PCB exposure may have adverse effects on the immune function in children therefore suggests that vaccine effectiveness may be an additional reason to prevent exposures to PCBs and other environmental pollutants.

Carsten Heilmann of the National University Hospital in Copenhagen, Denmark, was the lead author of the study. The Faroese cohorts were established by Chief Physician Pal Weihe in the Faroe Islands, in cooperation with Dr. Grandjean.

The work was supported by the National Institute of Environmental Health Sciences, the U.S. Environmental Protection Agency, the Danish Medical Research Council, and the Danish Environmental Protection Agency.