Are flu shots safe for young children?

Victoria Clayton • E-mail

While other people may be concerned about the shortage of flu shots, parents of young children have a completely different issue to ponder: whether or not to even get their kids vaccinated.

The government recommends that children ages 6 months to 23 months and others in high-risk categories get vaccinated. But many parents are confused about the safety and long-term repercussions of the vaccine on their children. In particular, they are concerned about thimerosal, a form of mercury used in small amounts as a preservative in most flu vaccines.

Some researchers and patient advocacy groups have long charged there is a possible link between thimerosal and autistic spectrum disorder. Thimerosal is used as an antibacterial/antifungal agent in a variety of medications, such as throat and nose sprays, and even contact-lens solutions. And, since the 1930s, it's been used as a preservative in many vaccines, enabling manufacturers to offer the drugs in larger vials, which can be used to vaccinate several patients instead of just one.

Compound banned from childhood vaccines
In the late 1990s, the U.S. Public Health Service and the American Academy of Pediatrics agreed that as a precautionary measure, vaccines given to children should be thimerosal-free or contain only trace amounts of the preservative, explains Dr. Julia McMillan, professor of pediatrics at Johns Hopkins University and a member of the American Academy of Pediatrics committee on infectious diseases. By 2003, all early childhood vaccines in the United States were thimerosal-free. Except, that is, for the flu vaccine.

Of course, any parent would wonder why the flu shot with thimerosal is supposedly safe for kids when the other vaccines that contained the chemical were not considered safe. According to McMillan, it wasn’t that thimerosal was ever considered unsafe; it was removed solely because there was a lack of information about its safety.

“When we made the recommendation it was because we just didn’t have enough information about mercury. The FDA was reviewing it for use in dentistry, drugs and so forth. We decided since more children were getting more vaccines and being exposed to thimerosal at a rate we hadn’t considered before, it would be best to minimize the exposure as a precaution,” she says.

Ethyl mercury vs. methyl mercury
While we know that mercury exposure causes neurological disorders and that humans should limit their exposure, the real risk comes from a form of mercury called methyl mercury, says Dr. Robert Roberts, an immunologist and professor of pediatrics at the UCLA School of Medicine. Thimerosal contains ethyl mercury, a different form of the chemical. Ethyl mercury is metabolized differently than the toxic methyl form and excreted quickly.

Chart Are your child's shots up-to-date?

“Chemically, the way the mercury (in the flu shot) is bound, it just can’t be utilized by the body like other forms of mercury,” says Roberts. “That’s why the flu shot is perfectly safe.” 

Roberts says, however, that it makes sense that parents of children with autism are looking everywhere — even to vaccinations — for potential answers.

Dr. Wilbert Mason, professor of clinical pediatrics at the University of Southern California School of Medicine and head of the division of infectious diseases at Children’s Hospital Los Angeles also says he understand why parents cringe at the thought of any sort of mercury — even a minute amount of the innocuous type — being injected into their children’s veins. But, he says, according to the latest science, the pain from the shot is the worst thing about it.

Teams of top researchers in the United States and elsewhere have failed to find any link between vaccinations with thimerosal and autism spectrum disorder, says Mason.

This year the Institute of Medicine released an exhaustive survey of published and unpublished studies looking for a possible link between thimerosal and autism. The report, called "Immunization and Safety Report: Vaccines and Autism," found no link. Studies published in the Sept. 2004 issue of the journal Pediatrics concurred with the findings. Interestingly, Mason notes that a well-regarded Danish study found not only no risk to children from thimerosal, but, ironically, a statistical benefit.

“In Denmark, thimerosal was removed from vaccines in the early to mid-‘90s,” explains Mason. “They have a very tight health-care system with a national database so there’s no question about the dose and the fact that the children received it. Analysis of their data showed no association between thimerosal and autism. In fact, they found a negative association. They actually found less autism in the children who were given the vaccines with thimerosal than without,” says Mason.

This finding probably doesn’t mean that thimerosal protects against autism; it more likely means that the number of children diagnosed with autism has risen in Denmark as it has here, adds Mason.

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