September 1, 2006

Pollutants may curb efficacy of childhood vaccines

By Will Boggs, MD

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.