PCB Exposure Attenuates Two Vaccines' Efficacy

ODENSE, Denmark, Aug. 24 -- The potency of diphtheria and tetanus vaccination can be attenuated by children's exposure to the pollutant polychlorinated biphenyl (PCB), according to researchers here.

Early PCB exposure was the major contributor to impaired antibody production in response to diphtheria and tetanus vaccinations, which may indicate a need for stepped up immunization in children at higher exposures, found a study sponsored by the U.S. and Danish Environmental Protection Agencies.

Every doubling in total PCB exposure reduced antibody response to the diphtheria vaccine by nearly a quarter in younger children and reduced tetanus vaccine response similarly in older children, Philippe Grandjean, M.D., of the University of Southern Denmark here and Harvard, and colleagues reported online on Aug. 22in the Public Library of Science Medicine.

Although most of the children made enough antibodies to both vaccines to provide protection, about a fifth of the older children had low levels of diphtheria antibodies, particularly those with the highest exposure, the investigators wrote.

The prospective study included two cohorts of children born in the Faroe Islands of Denmark, where PCB levels, but not dioxin, are known to be high, in part because whale blubber is a traditional food.

In one group of 129 children who received booster shots at age five, in addition to earlier vaccination, specific antibodies against tetanus were significantly lower in those whose mothers had above average serum PCB levels during pregnancy (4.61 versus 7.03, P=0.035). Immune response to the diphtheria vaccine was slightly lower for these children who were examined when they were 7 years old (0.60 versus 0.64, P=0.82).

Two years after the booster shots, a "surprisingly high" 21% (95% confidence interval 14% to 28%) of these children had diphtheria antibody concentrations below the 0.1 IU/mL limit necessary for long-term protection.

In the second group of 119 children who were tested at 18 months old, diphtheria vaccination was significantly less effective in those who had above average serum PCB levels during early childhood (1.37 versus 2.39, P=0.032).

The older children had no significantly differences in response based on early childhood PCB levels. The younger children had no significant differences in antibodies to either vaccine according to exposure before birth.

Though there were some differences between these cohorts, "the results are in overall agreement," Dr. Grandjean and colleagues wrote, and taken together suggest that the early postnatal period is most important in determining PCB's effects on the developing immune system.

The "crude picture of the exposure profile" painted by the few blood and milk samples taken for each child and mother pair may underestimate the true effect of the PCB exposure, the researchers said.

All results were controlled for gender, age, birth weight, whether the mother smoked during pregnancy, and time from last vaccination. None of the vaccines administered contained mercury-based preservatives, and mercury was not found to be associated with the immune response to vaccination.

The results may have implications for children around the world, the investigators said.

"Although the Faroese population has a substantially increased PCB exposure," the investigators wrote, "the results of the present study suggest that possible adverse influences on the immune function may well occur also at lower exposure ranges prevalent worldwide."

The study 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.