NEW YORK (Reuters Health) - Exposure to polychlorinated biphenyls (PCBs) -- chemicals widely used in industry -- apparently reduces children's immune response to vaccinations, according to a report.

"Pollutants, such as PCBs, may be partially responsible that vaccinations don't 'take' in some children," Dr. Philippe Grandjean from the University of Southern Denmark, Odense, told Reuters Health.
"I believe that this is yet another reason to protect children -- and pregnant women -- against chemical pollutants."

Grandjean and colleagues examined vaccination responses in two birth cohorts from the Faroe Islands where average PCB exposures vary widely and are up to 10-fold higher than average levels in Northern Europe "because traditional diets may include whale blubber contaminated with PCBs."

PCB exposure was determined by analyzing the mother's blood while she was pregnant and her early or "transition" milk, and by analyzing children's blood samples.

Among 119 children who received the standard diphtheria and tetanus vaccines and were examined at 18 months, there was a significant negative correlation between prenatal PCB exposure and antibody concentrations, especially for diphtheria, the authors report.

The higher the level of PCB exposure, the lower the antibody protection.

Similar results were seen in 129, 7-year-olds exposed prenatally or postnatally to PCBs, the results indicate.

Although most children had antibody levels sufficient to protect them against diphtheria and tetanus, the researchers note, 21 percent of 7-year-olds had diphtheria toxoid antibody concentrations below levels needed for long-term protection.

The antibody response to diphtheria toxoid at 18 months decreased by 24.4 percent for each doubling of the combined prenatal PCB exposure variable, the report indicates, and postnatal exposure had similar significant effects.

The investigators have "support from the National Institute for Environmental Health Sciences and US EPA to examine a larger group of 500 PCB-exposed children before and after the booster vaccination at age 5 years and then again at age 7," Grandjean said.

Many substances other than PCBs are known to toxic to the immune system in experimental animals, he added. "We need to take this information seriously and prevent human exposures."

SOURCE: PLoS Medicine August 2006. Source: http://www.planetark.com/dailynewsstory.cfm/newsid/37934/story.htm