New epidemiological evidence suggests that exposure to environmental pollutants may have an adverse impact on immune responses to childhood vaccinations. The research appears in the Aug. 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 age 18 months and 7 years, 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 for each doubling of the PCB exposure. At 7 years, the tetanus antibody response showed the strongest response and decreased by 16 percent for each doubling of the prenatal exposure.
"Our study raises concern that exposure to PCB and similar compounds may make childhood vaccinations less efficient," said Philippe Grandjean , adjunct professor at Harvard School of Public Health and co-author of the paper. Exposed children may also be more susceptible to infections in general, he said.
There were some limitations to the study, including the relatively small numbers of children who were examined and the time intervals between collection of blood samples. PCB is present in fatty fish worldwide and is known from laboratory studies to affect the development of the immune system. The 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 National University Hospital in Copenhagen, Denmark, was lead author of the study. The Faroese cohorts were established by Chief Physician Pál Weihe in the Faroe Islands, in cooperation with Dr. Grandjean.
The work was supported by the National Institute for Environmental Health Sciences, the U.S. Environmental Protection Agency, the Danish Medical Research Council and the Danish Environmental Protection Agency.
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