The concern about vaccinations is due to the fact that many of them require the use of a preservative that contains mercury. Thimerosal has been used as a preservative for many vaccines since the 1930s--even before the Food and Drug Administration required the use of preservatives (IVS). Preservatives are needed in immunizations to prevent bacterial or fungal contamination in multiple dose vials. This need was noted specifically in cases like one in Australia in 1928. Twenty-one children were given a vaccine, and eleven of those children died because of an injection of living staphylococci. The FDA mandated the use of preservatives in immunizations in 1968 after several such incidents.
The problem with this requirement is that thimerosal, the most widely used and most safely effective preservative, is 50% mercury by weight. Although the concentration of mercury within thimerosal is just a trace quantity at .01%, it amounts to 25 micrograms in one .5mL dose of a vaccine. This is within the safe levels of mercury designated by the FDA, however children are receiving more vaccines during infancy now than when those designations were made. Also, while many studies have been done on the effects of methylmercury on children's health, little research has been done on ethylmercury, the compound in thimerosal.
Methylmercury is a neurotoxin and has been shown to be responsible for cognitive deficits involving attention, language, motor, and sensory developmental delays. Because of these risks, the Environmental Protection Agency calculated safe levels of methylmercury to be 0.1 micrograms per kilogram of body weight per day. A series of studies of children conducted by Philippe Grandjean in the Faroe and Seychelle islands are still being conducted in order to determine whether or not the safe level needs to be changed. Pregnant women who ate whale meat containing methyl mercury in these studies consumed four times the safe dosage. This resulted in minor neurological deficits in the children of these women when they were tested seven years later.
Because of the lack of data defining the differences in risks between ethyl- and methylmercury, the FDA considers them equivalent when deciding safe levels within food and vaccinations. There are few studies of thimerosal specifically, and those that do exist offer little conclusive evidence. In 1931, Powell and Jamieson issued up to 26 mg/kg (micrograms per kilogram of body weight) to subjects with no reported toxic effects. The reports of mercury poisoning that the FDA was able to find resulted from a range of 3mg/kg to several hundred mg/kg of ethylmercury. The toxic effects in these cases were local necrosis, acute hemolysis, acute renal tubular necrosis, and central nervous system injury resulting in coma or death. An EPA study by Mendola, et. al., showed that high levels of exposure to methylmercury produced mental retardation, cerebral palsy and visual and auditory deficits in children (Mendola P, Selevan SG, Gutter S, Rice D. "Environmental factors associated with a spectrum of neurodevelopmental deficits." Mental Retardation And Developmental Disabilities Research Reviews Vol. 8, No. 3, 2002. 188.). It is important to note that these are not symptoms that closely resemble those of autism spectrum disorders. A 1985 study by Magos compared methylmercury and ethylmercury directly. Magos concluded that ethylmercury was less neurotoxic, although no quantitative comparisons were provided. Additional concerns that infants may not be able to eliminate ethylmercury from their systems as adults do were addressed in studies by the National Vaccine Advisory Committee that showed infants excreted mercury into their stools as well as adults.
The recent concern about thimerosal in vaccines arises from several different factors. The number of vaccinations infants receive in the first two years of life has gone from 8 to up to 20 since the early 1990's (Allen, 2002). Coinciding with the rise in the number of vaccinations is the number of cases of autism. A University of California, Davis study recently confirmed this rise and could offer no explanation as to its cause. From 1987 to 1998, the rate of autism has increased 273 percent, and the UC Davis study showed that it could not be attributed to misclassification or changing diagnostic criteria. Studies including the rest of the world have found that before 1985 the prevalence of autism was 4-6 per 10,000 children. Between 1985 and 1995 studies by the Centers for Disease Control and Prevention showed a prevalence of 11.8 per 10,000 children, and up to 1 in 500 were affected by some form of an autism spectrum disorder. The CDC also notes that during the time the increase in California was measured, other developmental disorders increased less than fifty percent. These factors, combined with a few well-publicized testimonials from parents who noticed their children's autistic symptoms shortly after immunizations, have led to suspicions of a link between vaccinations and autism spectrum disorders (Shattock and Savery, 1997).
These suspicions are certainly not unfounded, but have resulted in no evidence that a causal relationship exists between vaccinations and autism. The known symptoms of mercury poisoning and those of autism, while similar, are certainly not the same. The CDC states the symptoms of autism and other pervasive developmental disorders as follows:
Social skills: Children with ASDs do not interact with other people the way most children do, or they may not be interested in other people at all. Children with ASDs may not make eye contact and may just want to be alone. They may have trouble understanding other people's feelings or talking about their own feelings. A child with an ASD may not like to be held or cuddled and may not form the usual attachments or bonds to other people.
Speech, language, and communication: About 40% of children with ASDs do not talk at all. Other children have echolalia, which is when they repeat back something that was said to them. The repeated words might be said right away or at a later time. For example, if you ask the child, "Do you want some juice?" the child repeats "Do you want some juice?" instead of answering your question. Or a child may repeat a television ad he heard sometime in the past. Children with ASDs may not understand gestures such as waving goodbye. They may say "I" when they mean "you" or vice versa. Their voices may sound flat and it may seem like they cannot control how loudly or softly they talk. Children with ASDs may stand too close to the people they are talking to, or may stick with one topic of conversation for too long.
Repeated behaviors and routines: Children with ASDs may repeat actions over and over again. Children may want to have routines where things stay the same so they know what to expect. They may have trouble if family routines change. For example, if a child is used to washing his face before he gets into his pajamas, he may become very upset if he is asked to change the order and put on his pajamas first and then wash his face.
Some symptoms of mercury poisoning, such as developmental delays in language and attention, are similar to those of autism. However, the unusual symptoms that distinguish autism spectrum disorders from other developmental disorders, such as the social and sensory aspects of the disease, are not accounted for by what we know about mercury poisoning.
In fact, the main support for the link between vaccinations and autism seems to be the large number of case studies of children who were diagnosed with autism after receiving vaccinations. Safe Minds, or Sensible Action For Ending Mercury-Induced Neurological Disorders, presents myriad accounts of parents claiming that vaccines are responsible for their children's autism. Most of these case studies are similar to the following one published in NurseWeek and posted at www.safeminds.org:
After giving birth to her son, Lyn Redwood, MSN,FNP, of Tyrone, Ga., and her physician-husband tracked his development up to 15 months. After a series of vaccines, the boy started to regress, so Redwood had him tested. The diagnosis: severe developmental delay.
Redwood began to investigate the vaccines that preceded the diagnosis and found that all contained thimerosal, a preservative containing 49.6 percent ethylmercury by weight. By examining her son's records, she found that he had received 237.5 micrograms of ethylmercury in the first 18 months of life.
"I sent a piece of my son's baby hair for mercury testing and it came back with a report stating it contained 4.8 parts of mercury per million," Redwood said. "That's five times the allowable level for mercury. Research studies of children in the Faroe Islands whose mothers were eating mercury-contaminated seafood during pregnancy reported blood levels of 15 to 30 micrograms at birth, resulting in developmental delay. So I started looking at all the diagnostic markers for autism and found all those diagnostic markers to mercury. Looking back at it now, my son's symptoms for mercury poisoning were classic. My husband's a physician and he didn't see it, and I'm a nurse practitioner, but I had never seen a child with mercury poisoning."
Thimerosal - scientifically associated with a number of neurological disorders including autism, attention deficit disorder, speech delays and tics - was originally determined to be dangerous and was recommended to be withdrawn from nonprescription products by FDA experts in 1982, Redwood said.
Although case studies such as this are rather compelling, several things need to be taken into account. First of all, there is no conclusive evidence that thimerosal, ethyl-, or even methylmercury is associated, "scientifically" or in any way other than circumstantially, with autism, ADHD, or many of the other problems these case studies mention. In a 1999 study by F. Edward Yazbak, 25 out 240 women who received the Measles-Mumps-Rubella vaccine postpartum reported problems in their children ranging from autistic symptoms to gastrointestinal problems to future miscarriages.
Also, many of these case studies offer quantitative measures of the mercury both in the vaccines to which the children were exposed and in hair samples. However, they don't offer measures from children who weren't diagnosed with autism after their vaccinations. Given that most children receive the same immunizations, and that the FDA guidelines for safe levels of ethylmercury are based on its supposed equivalency to methylmercury rather than actual knowledge of its effects, these quantities are meaningless.
This works in the other direction as well. A recent study at the University of Rochester Medical Center concluded that the mercury in vaccines is at safe levels. This is reassuring, but does not take into account the fact that the FDA is currently reexamining exactly what those safe levels should be. However, it does provide even more evidence that the mercury from immunizations is eliminated from the blood quickly, even in infants.
There is certainly cause to investigate the effects of thimerosal on children due to knowledge of the effects of methylmercury, growing knowledge of the effects of ethylmercury, and the increased amounts of ethylmercury received by infants in the 1990s. However, there is certainly no conclusive evidence to suggest that vaccines are directly responsible for the increased rates of autism. The Immunization Safety Review Committee at the Institute of Medicine states that although the hypothesis is biologically plausible, the evidence is inadequate and neither proves nor disproves the theory. Even the aforementioned Dr. Halsey himself denied that he believes in that vaccinations cause autism, saying that The New York Times Magazine misrepresented his position.
Regardless of whether or not vaccines cause autism, the questionable levels of safety are enough cause to find ways to preserve vaccines without the use of mercury. The rise in autism cases is certainly cause for more research in this area. For now however, the certain risk of getting a disease that could cause death is more urgent than the unknown risk of developing autism, so getting a child immunized is still most likely the best option for parents.