Hundreds of thousands of infants and toddlers who get flu shots starting this fall could be exposed to a mercury-laced preservative that has been all but eliminated from other pediatric vaccines because of health concerns.
Saying there is no proof of harm from exposure to the preservative thimerosal, officials with the U.S. Centers for Disease Control and Prevention have confirmed that they won't advise parents and doctors to choose a mercury-free version of the flu vaccine.
This year, flu shots are being added to the government's "recommend" list of vaccines that should be given to all young children. The CDC's decision on thimerosal, made despite pleas from parent activist groups and some experts, appears to be at odds with recent federal warnings about exposure to mercury, a potent neurotoxin, and with the government's successful effort to have it removed from other childhood vaccines.
The mercury-free flu vaccine will be more expensive -- by about $4 per shot -- and is somewhat harder to make in large quantities than the alternative. If the CDC were to warn parents, demand for thimerosal-free shots would rise, possibly squeezing supplies. Some experts said a shortage could lead to some children not being immunized against a known risk, flu, in order to avoid the theoretical risk of thimerosal.
"The available scientific evidence has not shown thimerosal-containing vaccines to be harmful," the CDC said.
The American Academy of Pediatrics, which has a membership of 57,000 physicians, is backing the CDC.
But the agency has come under blistering attack from some parent groups. By not advising parents and physicians, the government is "violating the precautionary principle which reminds doctors that, when in doubt, take an action which minimizes the risk of harm," said Barbara Loe Fisher, co-founder of the National Vaccine Information Center, a parent-led group that promotes safer vaccines.
Rep. David Weldon (R-Fla.) said he planned to introduce a bill to ban thimerosal in childhood vaccines. The CDC's refusal to recommend mercury-free shots "is medical malpractice," Weldon said. A physician with a young son, he said he wouldn't let the child have a shot containing mercury.
Preservatives are used by drug companies to prevent the growth of bacteria and fungi in vaccines. Thimerosal, which is nearly 50% ethyl mercury, had long been the preservative of choice. That changed in 1999, when the U.S. Public Health Service and the academy of pediatrics called on drug firms to voluntarily remove thimerosal from pediatric vaccines as a precaution.
In doing so, they acknowledged a major oversight: Under the country's increasingly aggressive policy of childhood immunizations, infants were being repeatedly exposed to mercury in cumulative doses far above Environmental Protection Agency guidelines.
Since then, vaccine producers have virtually eliminated thimerosal from regularly scheduled childhood vaccines.
Some parent groups and researchers believe that thimerosal has contributed to a sharp increase in reported rates of autism and other developmental disorders in children. Nearly 4,000 compensation claims have been filed in a special vaccine injury branch of the U.S. Court of Claims on behalf of children with autism-related disorders.
Vaccine makers and many scientists dispute the connection, contending, among other things, that the exposures are too low and that ethyl mercury is more easily eliminated from the body than methyl mercury -- the type produced by industrial emissions that ends up in fish.
The CDC's neutrality on thimerosal in flu vaccines comes amid blunt warnings from other federal agencies about reducing methyl mercury levels in infants and toddlers, whose developing brains may be more vulnerable.
Last month, for example, the Food and Drug Administration cautioned that young children and women who are nursing or pregnant should avoid fish high in mercury, such as shark and swordfish. In February, the EPA estimated that nearly 1 in 6 babies may be exposed to hazardous levels of mercury through the umbilical cord.
In recent months, small mercury spills resulted in the evacuation and cleanup of several schools. In January, for example, a middle school in Reno was shut down for eight days of extensive decontamination after mercury spilled on a school bus was tracked inside by students.
Boyd E. Haley, who is chairman of the department of chemistry at the University of Kentucky and is considered an authority on both ethyl and methyl mercury, said it was "preposterous and ridiculous" for the government to warn about methyl mercury in fish but sanction ethyl mercury's being injected into children.
The CDC decision is "unconscionable," Haley said. "If it were my grandson or my granddaughter, there's no way in hell you'd give them a vaccine containing thimerosal."