Apples and Oranges: Science Debunks Autism-Vaccine Link

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Science Feature - September 2005  

By  Ken Ortolon
Senior Editor  

Cynthia Singleton hesitated to immunize her newborn son in 1998. In fact, she waited more than a year before he was vaccinated because of some complications, and she wanted to make sure he was developing normally.

Now, the Houston mother regrets having her son vaccinated at all because within a few weeks he began exhibiting behavior she says were the first signs of autism.

Since the late 1990s, a debate has raged over whether childhood vaccines -- and, more specifically, a mercury-based preservative in vaccines called thimerosal -- are responsible for soaring rates of autism in children.

A vocal group of parents is convinced that increased exposure to mercury from a growing list of recommended vaccines is causing neurodevelopmental problems in children. Scientists, however, say the evidence of such a causal link just doesn't stack up.

Vaccine critics refuse to trust scientific data, and in June, an article by an environmental lawyer with a famous name fanned the flames even further with allegations of a cover-up by U.S. health officials and pharmaceutical interests to hide the damage that thimerosal has done.

While scientists sympathize with parents of children with autism, they say negative publicity about vaccines may cause greater harm.

"It's perfectly appropriate for them to ask questions about vaccine safety," said Martin Myers, MD, associate director for vaccine policy and education at the Sealy Center for Vaccine Development at The University of Texas Medical Branch at Galveston. "But so much hype and so much misinformation is confusing parents. Some of them are confused enough that they're not sure what to do, so they hesitate. And it can have tragic results as a consequence." 

Looking at the Science  

Thimerosal was used as a preservative in vaccines for decades, but concern over the amount of mercury to which newborns were being exposed through vaccines began to grow with the list of recommended childhood vaccines. In 1999, the United States followed the lead of several European countries and ordered thimerosal removed from childhood vaccines, pending safety studies.

In 2000, the U.S. Centers for Disease Control and Prevention (CDC) asked the Institute of Medicine (IOM) to review existing data on the potential thimerosal-autism link. In 2001, IOM concluded there was insufficient data to accept or reject claims against thimerosal, but that a biological link to neurodevelopmental disorders was "plausible."

By 2004, however, a substantial body of new research on thimerosal was available. In May of that year, the IOM declared that a causal link between thimerosal and autism should be rejected.

While Dr. Myers says most people in the scientific community view the IOM as being "about as good as you can get," its conclusions did not put the controversy to rest. 

Conspiracy Theories  

Almost immediately, anti-thimerosal groups such as the parent-led National Vaccine Information Center criticized the IOM conclusions, claiming it had compromised its independence and integrity.

And in June, attorney Robert F. Kennedy Jr., published an article on and in Rolling Stone magazine charging that CDC, IOM, and others colluded with vaccine makers to whitewash the issue. Mr. Kennedy accused health officials of meeting at an isolated conference center in Georgia to plot their cover-up with pharmaceutical manufacturers. He also contends the CDC directly ordered the IOM to reject the thimerosal-autism link.

Over the next several weeks, Mr. Kennedy's article prompted a war of words among himself, IOM, and others. In a letter to, IOM President Harvey V. Fineberg, MD, PhD, accused Mr. Kennedy of misrepresenting the purpose of the IOM studies by "selectively using and fabricating quotations" from transcripts of an organizational meeting of the IOM Vaccine Safety Committee.

IOM spokesperson Christine Stencel says the IOM's refusal to rule out a link between thimerosal and autism in 2001 debunks Mr. Kennedy's claim.

"The committee in 2001 said we can only say what the available evidence enables us to say, not what any individual or group wants us to be able to conjecture from the evidence," she said. "And what the evidence allowed them to say in 2001 regarding thimerosal was that there's too little to say one way or the other."

Dr. Myers, former director of the U.S. Department of Health and Human Service's National Vaccine Program Office and now executive director for the Galveston-based National Network for Immunization Information (NNii), attended the Georgia conference. He says Mr. Kennedy and others have drastically distorted the discussions by scientists and health officials.           

"They've taken discussions out of context and done some pretty damning things with it," said Dr. Myers, whose NNii is dedicated to correcting misinformation about vaccines. "If you actually read the transcript [of the Vaccine Safety Committee organizational meeting], it's a bunch of serious people talking about just exactly what it is they were being charged to do and trying to understand it," he said. "Those kinds of conversations go on all the time in scientific forums when people start to try to get a grasp on what it is they are being asked to evaluate."

Vaccine supporters say every reputable study on thimerosal backs up the IOM conclusions. Plus, studies show autism rates in Finland and the United Kingdom -- two of the first nations to remove thimerosal from vaccines -- continue to climb.

A report published this year in Current Directions in Psychological Science suggests rising autism rates may stem from better recognition and reporting, as well as an expanded definition of what constitutes autism. And a 2005 study from The University of Texas Health Science Center at San Antonio suggests that environmental mercury released by coal-burning power plants might be to blame. 

Redirecting Research  

Still, opposition to vaccination persists. Ms. Singleton dismisses the notion that thimerosal has been removed from or reduced to only trace amounts in childhood vaccines. She refuses to have her second child immunized.

But Dallas pediatrician Pablo Sanchez, MD, says he has confidence in the IOM's credibility. He believes parents should feel good about getting their children vaccinated.

"The IOM concluded there was no known association. The vaccines no longer contain thimerosal, so that should not be an issue," said Dr. Sanchez, chair of the Texas Pediatric Society (TPS) Committee on Infectious Diseases and Immunizations.

Both scientists and pediatricians are concerned that the continuing controversy may detract from efforts to identify true causes of autism.

"Autism is a devastating disorder, and we need to do all we can to find the causes and remove them," said San Angelo pediatrician Jane Rider, MD, TPS president.

Dr. Myers says autism research, however, needs to move on to other areas. "The Institute of Medicine said it's now time to focus what resources we have for autism research on a more fruitful area than a linkage with thimerosal. They made that point because autism and autism spectrum disorder is so important medically that we need to understand it better. We should be spending money on it, but the kinds of studies trying to look for some linkage to thimerosal the data now suggests are not likely to be fruitful. Let's go on and look for other things."

Ken Ortoloncan be reached by telephone at (800) 880-1300, ext. 1392, or (512) 370-1392; by fax at (512) 370-1629; or by email at  Ken Ortolon.  


Latest Research on Vaccines and Autism Available Online

Physicians are the first people parents turn to for information that affects their children's health, and public health officials want to make sure physicians are well-armed with facts. And there is a plethora of information available on both government and private Web sites.

On the heels of the June publication of an article alleging a vast cover-up of a link between autism and thimerosal, the Texas Department of State Health Services (DSHS) sent physicians an alert with information that may be helpful in answering parents' concerns about thimerosal.

"We just want health care professionals to have as much information as they can have," said Jack Sims, manager of the DSHS Immunization Branch. "If immunization rates are affected by this, we don't want it to happen because of a lack of information among the health care community."

The DSHS alert pointed out that the mercury in thimerosal -- ethylmercury -- has highly different properties than methylmercury, the more common form of organic mercury. Methylmercury, in high doses, can adversely affect the nervous system.

But new studies published just this year show that ethylmercury is metabolized and excreted quickly and does not accumulate in the body the way methylmercury does, says Martin Myers, MD, associate director of vaccine policy and education at the Sealy Center for Vaccine Development at The University of Texas Medical Branch at Galveston and executive director of the National Network for Immunization Information (NNii).

NNii was created to respond to misinformation about vaccines and maintains an extensive review of current literature on vaccine safety on its Web site at

"The intent was to be evidence-based," Dr. Myers said. "We're not an advocacy group. If you have questions about vaccines -- good, bad, or indifferent -- this is the place you can come for nontechnical, evidence-based information."

The U.S. Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) also have information regarding research on autism and thimerosal on their Web sites. Information from CDC can be found at, and the AAP Web site can be found at

Institute of Medicine reports on the potential link between thimerosal and autism can be found at

All of these links -- and additional information -- are available from the  TMA Immunization Resource Center.

Finally, physicians also can contact the DSHS Immunization Branch for additional information at (800) 252-9152. 


Vaccine Safety: Myth Versus Reality

Immunization is one of the greatest public health success stories of the 20th   century. In fact, immunizations have saved more lives and prevented more disease than any other single medical success.

Vaccines promote health, reduce unneeded hospital visits, and save lives. Without immunizations, children, unborn children, pregnant women, and other adults are at risk of catching diseases that cause choking, paralysis, brain injury, and death.

Be Wise - Immunize, the joint immunization awareness campaign of TMA, the TMA Alliance, and the TMA Foundation, offers the following information you can use to counter arguments against immunization. The information is based on numerous scientific studies published in medical literature. 

Myth:  Because most of the vaccine-preventable diseases are rare or have been eliminated, there is no longer any need to vaccinate.

Reality:  Although several of the diseases that vaccines prevent have been dramatically reduced or eliminated, vaccines are still necessary. Numerous studies have shown that when immunization rates decrease, disease outbreaks occur. This happened in the late 1980s and early 1990s when thousands of children were hospitalized and more than 120 died. Some pathogens, like tetanus, are constantly present in the environment. And although some diseases have been completely eliminated (polio) or virtually eliminated (diphtheria) from this country, they still occur in other parts of the world. Because there is a high rate of international travel into and out of the United States, outbreaks of these diseases are only a plane ride away.

Myth:  It is not safe for young children to get so many shots at once.

Reality:  Newborns commonly encounter and manage many challenges to their immune systems at the same time. Some children can receive up to 20 shots by the time they reach age 2 years and may receive as many as five shots in a single visit. Upon birth, babies immediately face a host of challenges to their immune systems. Newborns are capable of responding to millions of different viruses and bacteria because they have billions of immunologic cells in their bodies. Therefore, vaccines given in the first two years of life are a tiny fraction of the substances an infant's immune system successfully encounters in the environment every day.

Myth:  Vaccines are not safe.

Reality:  Because vaccines are given to people who are not sick, they are held to the highest standards of safety. As a result, vaccines are among the safest substances we put in our bodies.

All vaccines have possible side effects. Most of these effects are mild, ranging from fever, tenderness, and swelling to rare instances of persistent crying, high fever, or seizures with fever. Although these reactions do not result in any permanent harm to children, they can be quite frightening. So, if vaccines cause side effects, wouldn't it be much safer to avoid them altogether? Unfortunately, avoiding vaccines involves choosing to take a greater risk. Discontinuing the pertussis vaccine in countries such as Japan and England led to a 10-fold increase in hospitalizations and deaths from pertussis. When you consider the risks of vaccines and the risks of diseases, vaccines are the safer choice.

Myth:  The measles-mumps-rubella (MMR) vaccine causes autism.

Reality:  Numerous carefully performed studies clearly disprove that the MMR vaccine causes autism. Because autism often may appear in the second year of life, at around the same time children receive certain vaccines, people have speculated that the vaccines might cause autism.

Studies conducted with large numbers of subjects have been conducted in the United States, the United Kingdom, and Denmark. All of these studies found that children with autism were no more likely to have received the MMR vaccine or to have received the MMR vaccine recently than other children. Although the cause or causes of autism remain unclear, several excellent studies of the structural abnormalities found in the brains of children with autism, the genetic make-up of children with autism, and the timing of the first symptoms of autism all lead to the same conclusion: Autism is likely to occur before birth.

Myth:  Vaccines contain preservatives and additives that are harmful.

Reality:  Many vaccines contain trace quantities of antibiotics and stabilizers; however, thimerosal, a preservative containing ethylmercury, has now been removed from all routinely recommended vaccines . Preservatives, antibiotics, and stabilizers are used during the manufacture of vaccines to prevent   contamination with bacteria or fungi. Without these additives, bacteria in a vial could then be inadvertently injected into the child, resulting in serious and occasionally fatal infections. While exposure of infants to high levels of environmental mercury (methylmercury) can be harmful, the levels of mercury (ethylmercury) contained in thimerosal were within established safety guidelines. In addition, ethylmercury is excreted from the body much more quickly than methylmercury and has not been detected in children inoculated with vaccines containing thimerosal.

This information is on the  TMA Web site  (search for "vaccine safety").

Physicians can get involved in the effort to increase the public's awareness of the need for immunizations of children and adults by joining the I'm Wise Panel. It lets you play an irreplaceable role in protecting your patients and others against preventable, infectious diseases. I'm Wise panelists tell the stories of their personal experiences or those of their family members or friends to the news media and civic groups to put a face on the sad statistics of Texas' low immunization rates.

If you're interested, send an email to  or call (800) 880-1300, ext. 1470, or (512) 370-1470. 


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