Our goal is to simplify the information gathering and evaluating process. Our approach is to provide multiple perspectives from leading authorities and varies websites on autism related topics. This will provide our readers the opportunity to gather multiple viewpoints from a single location and form the best-educated decisions for their family’s needs.
Disclaimer: The Autism Resource Foundation provides general information to the autism community. The information comes from a variety of sources, and the Autism Resource Foundation does not independently verify any of it, nor does it necessarily reflect the views and/or opinions of the Autism Resource Foundation. Nothing on this website should be construed as medical advice. Always consult your doctor regarding the needs of your family.
Autism and vaccines: It’s the link that just won’t die.
The American Academy of Pediatrics, the CDC, the World Health Organization, and the Institute of Medicine all agree that there’s probably no relationship between autism and vaccines.
But if the case is that solid, why do so many people remain unconvinced, from actress Jenny McCarthy, who went on Oprah to say she believes that a vaccination caused her son’s autism and wrote a book about it, to Sen. John McCain, who, at a campaign event earlier this year, said he thought there was “pretty strong evidence” that some vaccines cause autism.
Their beliefs may have been validated in March when federal officials said that a Georgia girl was entitled to compensation because vaccines may have aggravated an underlying condition, causing autism-like symptoms.
And researchers at the National Institute of Mental Health (NIMH) said in March that they are still taking a careful look into parent concerns that vaccines are tied to the disorder.
“I think there’s a lot of emotion around the issue of autism now. It engenders a lot of fear in parents and clinicians alike,” Lee Sanders, MD, MPH, associate professor of pediatrics at the University of Miami Miller School of Medicine, tells WebMD.
Sanders knows that emotion firsthand, as the father of two young girls. “Until they turned 2 or 3, that was probably the thing I feared most,” Sanders says, referring to autism.
Sanders strongly supports vaccines, saying their benefits far outweigh their risks. But he understands where the concern about vaccines and autism comes from.
That concern is difficult to suppress for a number of reasons. Parents are bombarded with information that can take a life of its own online. The concepts around scientific testing are difficult to understand, making it tough to separate good science from bad. Until scientists can prove exactly what causes autism, it’s difficult to definitively disprove anything.
“In the absence of any answers from the scientific community, any scintilla of suggestion is going to get magnified by the social process of talking it out,” Sanders says. “All you need is one individual’s story and it will expand.”
And when something bad happens to a child, people demand to know what or whom is to blame. “Parents are clamoring for a cause,” says David Tayloe, MD, a pediatrician in Greensboro, N.C., and president-elect of the American Academy of Pediatrics (AAP).
“It’s a terrible condition. It upsets families, and it upsets me.” But all the fear and anger about vaccines is misplaced, he says. “There’s just nothing there.”
Vaccine-Autism Disconnect: MMR Vaccine, Thimerosal
The main reason why anyone talks about vaccines and autism is that some parents have noticed changes in children shortly after the children were vaccinated. Their kids seemed to be developing normally, then suddenly stopped interacting with people and lost language abilities — a condition called “regressive” autism.
Most medical researchers argue that this is probably a coincidence: Autism symptoms tend to become apparent around the same time that children are scheduled to get routine vaccines.
Although there are two separate issues concerning vaccines and autism, they’re often lumped together. One has to do with the measles, mumps, and rubella (MMR) vaccine; the other involves vaccines containing the chemical preservative thimerosal, which contains a form of mercury that has been suspected of causing autism and has recently been removed from most vaccines.
The MMR scare started 10 years ago with a report published in The Lancet that described the cases of eight children who, as their parents recalled, developed autistic symptoms and digestive ailments shortly after getting their first MMR dose. The researchers proposed that the vaccine might trigger a previously unknown form of regressive autism. They suggested that maybe the measles virus in the vaccine lodged in the intestine, causing some kind of reaction that then affected the brain.
After that, experts studied whether the MMR vaccine could cause autism. To do that, they looked for clues among kids who did and didn’t get the vaccine.
Since that initial finding, 14 studies including millions of children in several countries consistently show no significant difference in autism rates between children who got the MMR vaccine those who didn’t.
The bottom line: It’s very unlikely that the MMR causes autism, researchers say.
Vaccine-Autism Disconnect: Complex Science
A lot of the confusion comes from the complexity of the science involved in the issue. “It’s hard to communicate in a way that’s unambiguously clear,” says Melinda Wharton, MD, deputy director of the CDC’s National Center for Immunization and Respiratory Diseases.
Scientists often hedge about saying whether their findings prove or disprove anything. That’s because the scientific method proceeds by constantly modifying theories rather than accumulating “proofs.”
Vaccine-Autism Disconnect: Complex Science continued…
But those who take issue with the scientific consensus that vaccines have very little to do with autism focus on research that seems to support their opinions. In particular, they point to the work done by Mark Geier, MD, PhD, a former researcher at the National Institutes of Health, and his son, David Geier, whose studies did show a strong link between autism and vaccines.
So who’s right? An Institute of Medicine panel reviewed all of the evidence on vaccines and autism in 2004. But the reviewers excluded the Geier studies, finding them “uninterpretable.” The AAP issued a statement explaining how the Geiers were probably wrong, listing 15 critical errors or omissions in just one of their studies.
Still, some activists believe that authorities are suppressing this evidence because it’s inconvenient, and the Geiers have never backed off from their conclusions. But experts say the basic flaws of their studies are glaringly obvious.
Marie McCormick, MD, a professor at the Harvard School of Public Health, oversaw the committee that conducted the 2004 IOM vaccine safety review and extensively reviewed their work. To begin with, she says, the Geirs used inappropriate data sources for their studies.
One study was based upon case reports in the CDC’s system for tracking vaccine side effects. Those reports can alert researchers to issues that deserve study. But they’re a far cry from the sort of evidence scientists need to prove something.
In addition, when researchers try to prove cause and effect, they use samples that reflect the general population. So using only data about people who got sick from vaccines isn’t generalizable.
Other studies done by the Geiers also had flaws, McCormick says. In one of them, the Geiers estimated a rate of autism in different groups of U.S. children based upon case records for government-sponsored special education programs. But because eligibility requirements vary from state to state, it’s unlikely that the special-ed rolls accurately reflect a real rate of autism.
What’s more, the Geiers made major errors with their calculations. “They didn’t understand how to analyze the data,” McCormick says. Such statistical flaws are fatal, but all that goes over the heads of many people. “If you stand up in front of an audience and explain that, you are going to look like a nerd,” McCormick says.
Vaccine-Autism Disconnect: The Mercury Question
As if the MMR vaccine wasn’t enough of a hot potato, other vaccines also caused concern.
When researchers started looking for a possible link between autism and the MMR, all other childhood vaccines came under scrutiny, too. In 1998, 30 different vaccines with thimerosal in them were given to children. U.S. public health officials realized that the recommended schedule of vaccines could give some children mercury that exceeded the limit considered safe by government standards.
In 1999, the U.S. Public Health Service and the AAP asked vaccine makers to reduce or remove thimerosal in vaccines. By 2001, all routine childhood vaccines were available thimerosal-free.
The 2004 IOM review included five large-scale studies that compared autism rates in vaccinated and unvaccinated children. These and other recent studies, including one published in TheNew England Journal of Medicine in September 2007, have shown that children who received vaccines with thimerosal are not more likely to have been diagnosed with autism than those that weren’t vaccinated or received less thimerosal from vaccines.
Sallie Bernard, founder of the advocacy group Safe Minds, tells WebMD that she doesn’t believe the results of epidemiological studies showing no link between autism and vaccines. “We say you have to look at the biology,” she says.
In her opinion, mercury poisoning and autism seem too much alike to rule out mercury as a cause. Mercury poisoning can cause brain damage, and symptoms can be similar to those of autism.
“I certainly wouldn’t argue that the only source of mercury and the only source of harm is the mercury in vaccines,” Bernard says. She says she believes children continue to be harmed by vaccines that still contain thimerosal.
But while Harvard’s McCormick agrees that mercury is a dangerous substance, the claim that mercury poisoning and autism are the same doesn’t hold up under scrutiny, she says. “It’s based on a very superficial similarity.”
Symptoms of mercury poisoning can include irritability, depression, anxiety, visual problems, speech problems, and sensory nerve problems. In autism, there can be findings of delayed speech, increase or decrease in response to sensory stimuli, and avoidance of human eye contact.
Vaccine-Autism Disconnect: Meet Ethyl and Methyl
Recently, basic assumptions about thimerosal have come into question that may further confuse any links to autism.
Thimerosal contains ethyl mercury. The government’s assessments of health risks for thimerosal are based on what is known about another chemical form of mercury, called methyl mercury.
The health assessments for methyl mercury are based on exposure by eating or drinking it. Warnings about eating certain kinds of fish, for example, are all about fish contaminated with methyl mercury.
Thimerosal, on the other hand, isn’t eaten; When experts called for reducing and removing thimerosal from vaccines in 1999, they assumed that methyl mercury and ethyl mercury were pretty much the same, and the health risks may be the same even though the way children are exposed is different. A study published in the journal Pediatrics in January 2008 shows that ethyl mercury leaves children’s blood faster than methyl mercury does, so the health risks may not be the same.
However, while it left the blood quickly, it doesn’t necessarily mean it left the body. While the study did show that the mercury did not damage the kidneys, for instance, it didn’t look at other organs.
Vaccines and Autism: Other Studies Under Way
Sue Swedo, MD, chief of the pediatric and developmental neuropsychiatry branch of the National Institute of Mental Health, says federal researchers have not closed the door to looking at whether vaccination might, in rare cases, be linked to autism.
The strongest case for a link comes from children with regressive autism — children who seem to be developing normally, but who then lose the social and language skills they had developed and slide into autism. To parents, such children seem to have been the victims of some environmental toxin. As this regression occurs at the same time children receive multiple vaccines, many wonder whether vaccines might carry such a toxin.
“Our studies of regressive autism are taking a very shotgun approach to environmental factors in autism,” Swedo tells WebMD. “We are saying we don’t really know right now whether such factors might be involved.”
Vaccines and Autism: Other Studies Under Way continued…
The Childhood Autism Risks From Genetics and the Environment (CHARGE) study is under way at the University of California, Davis. Funded by the National Institute of Environmental Health Sciences and enrolling more than 600 families with autism, this study is looking at the interplay between genetic and a wide range of environmental factors in autism. Vaccines are one of the many environmental factors being analyzed.
In addition, the CDC’s Centers for Autism and Developmental Disabilities Research and Epidemiology network (CADDRE) is collecting data on environmental risk factors, including vaccines, that might put children at risk of autism.
Using the same environmental-factor checklist as CHARGE and CADDRE, the NIMH is looking at differences between children with regressive autism and children with more classic forms of autism.
“We are looking at differences in environmental exposures, including vaccines but also including things like older brothers who had a cold and mothers who drank a lot of diet soda during pregnancy,” Swedo says.
The CDC and the NIH are also performing epidemiologic studies in Norway and Denmark to expand previous research into whether vaccinated children have any more autism than unvaccinated children.
“Neither [NIMH Director Tom] Insel or I are ready to discard the vaccine hypothesis, but we don’t think there is anything in vaccines that causes autism in the vast majority of cases,” Swedo tells WebMD. “In earlier cases where vaccines caused rare complications, we figured it out quickly. Since vaccines are given so often, if there was a strong connection between vaccination and autism we would know it by now. What we are not discarding is the one-in-ten-thousand or one-in-a-million cases that might have a link.”
Vaccines and Autism: High Stakes
The specter of autism frightens parents. But today few parents in the U.S. or other developed countries have seen the suffering and death wrought by measles and other disease that vaccines can prevent, including measles, tetanus, polio, diphtheria, whooping cough, and influenza. These diseases still afflict millions of children in places that vaccines don’t reach.
Every year, 2.5 million unvaccinated children worldwide die of diseases that vaccines could have prevented, and vaccines prevent the deaths of an additional 2 million children, according to the World Health Organization.
Vaccines and Autism: High Stakes continued…
History provides another perspective. “In the 1940s, the hysteria was, ‘My child is going to get polio, do something about this,’ and the scientific community developed the fist childhood vaccine and just about eradicated polio from the face of the earth,” says Sanders.
Most American children get their recommended vaccines, which are required for going to school. But a small minority of parents passionately oppose that requirement and probably always will.
“Even so, we’re not going to stop giving vaccines during that time,” the AAP’s Tayloe says. “We’re going to stick to the science.”
Still, Sanders shows why the debate is not likely to end any time soon. Even though he’s firmly in favor of vaccines, he doesn’t dismiss concerns about them outright.
“We’re going to continue to do the research to look for unknown side effects,” he says. “We’re not going to stop looking.”