Many parents have been asking whether vaccines have been linked to autism or to other neurologic or developmental disorders. This issue has received media attention over the past several years; however, it has received increased attention in 2007. One reason for the increased media coverage is the lawsuit before the federal Vaccine Injury Compensation Program began in the summer of 2007, representing over 5,000 families claiming that the mercury preservative, thimerosal, caused their child to develop autism. The other reason seems to be increased coverage on shows such as the Oprah Winfrey Show, as well as books written by celebrities. In April, 2007, Oprah did a show on autism and a possible link with vaccines was briefly discussed. In September, 2007, she did a show specifically on vaccines and autism, featuring actress Jenny McCarthy, who has written a book claiming that the MMR vaccine caused her son to become autistic.
There are two separate issues. One is whether measles vaccine causes autism. In 1998 a group of researchers in England who suggested a link between measles vaccine, intestinal disease and autism. The researchers reportedly discovered genetic code from the measles virus in the intestines of children with autism. The research was never confirmed, but this sparked a reaction in England and the United States, and other places as well I suppose. Since publication of this paper the issue has been extensively researched and no link has been found. Recently, it was shown that the labs made an error and on retesting the samples no measles genetic code was found. The prestigious journal that published the original paper later stated that they should not have published the paper the way that it did because the lead author had undisclosed conflicts of interest (with lawyers pursuing vaccine litigation). Most of the authors have also now retracted their interpretation of the findings that there may be a link between MMR and autism. Recently, the lead researchers have come under investigation for research ethics violations. Of course, these retractions have not been widely publicized, and the idea has persisted that there may be a link between MMR and autism.
There is no evidence that measles vaccine or MMR vaccine is linked to autism. The symptoms of autism usually appear around 18-24 months of age, and since the MMR vaccine is given around 12-15 months of age for the first time, it leads people to wonder if it may be the cause. It is a valid research question because the measles virus itself does sometimes infect the brain and cause disease, and the MMR vaccine contains live but modified measles virus. However, there never has been any evidence to link measles or MMR to autism.
What I don?t understand is the argument of Jenny McCarthy and others when they say, ?I gave my child MMR vaccine and watched him get autism.? This is no different than saying, ?I started giving my child milk and watched him get autism? or, ?He started walking and I watched him get autism.? Thousands of kids get MMR vaccine, drink milk, and start walking and don?t get autism. Some kids get MMR or drink milk and get autism. Meanwhile, some kids with autism never drank milk or got the MMR vaccine. Not only is this kind of argument not scientific, it is not even logical. Everyone who has gotten autism also drinks water. Does drinking water therefore cause autism? Of course not. To scientifically prove that one thing causes something else, first there must be an association. The two things must be present together and absent together. They must be associated with one another. That has not been shown here. Even if things are associated with each other, this does not show cause. More careful research that controls for other variables and factors must be done to show if one thing causes another. There is no more evidence for an association or a cause between MMR vaccine and autism than there is for milk drinking and autism. There is just no evidence there.
A second issue and one that may be more logical in my opinion is that of thimerosal, the mercury-based preservative used in many vaccines in the United States until recently and still used in vaccines in other countries. Thimerosal is an ethylmercury compound and is not related to the mercury found in fish and other environmental toxins, which is methylmercury. Ethylmercury is excreted from the body and shows no signs of being a neurotoxin; methylmercury, on the other hand, is an environmental toxin that concentrates in animal tissues (such as fish) and causes neurologic damage. Thimerosal has been used since the 1930s as a preservative in vaccines. In 1999, the FDA basically recalculated how much thimerosal children were getting with the increased number of vaccines being given. They calculated a dose of 187.5 micrograms by 6 months of age. They then looked at their own data as well as that of the EPA and discovered that there were no safety guidelines for ethylmercury exposure. Scientists from the CDC, the EPA and the American Academy of Pediatrics met to discuss the findings and also the fact that there were no data comparing neurologic outcomes in children who received thimerosal with those who had not. The panel decided that in the absence of data it might be prudent to use a different preservative. The panel asked vaccine manufacturers, as a precaution, to remove thimerosal from vaccines. They also asked doctors and hospitals to delay the birth dose of hepatitis B vaccine in children who were not at risk for hepatitis B. Manufacturers stopped using thimerosal in almost all childhood vaccines by 2001. The panel stated that current levels of thimerosal were safe, but reducing it would make vaccines even safer, which was a somewhat confusing statement.
This sparked a large reaction in the United States, with advocacy groups springing up in 2000 and parents reporting their child?s autism to the Vaccine Injury Compensation Program because the child had received thimerosal-containing vaccines. There was also a great deal of confusion in the public and among doctors, particularly since the panel said thimerosal doses were safe but removing them would be even safer, a seeming contradiction. It led to some infants not receiving a needed hepatitis B vaccine with at least one death. It also led to a new industry of mercury chelation, again with some deaths from the chelation agents. The American Academy of Pediatrics again added to the confusion in 2001 when its Committee on Environmental Health stated that ?mercury in all its forms is toxic to the fetus and children.? This statement included thimerosal; ethylmercury can be toxic at high doses, but there has been no evidence of toxicity from the doses in vaccines. All of this reaction in the public and the media has been based on a precaution taken by experts. There were no studies, no research, and no data suggesting any harm from thimerosal in vaccines. While I agree that it may be prudent to remove it from the vaccines, there is no logical reason to assume that it causes autism or any other disease for that matter.
There was and is no evidence that thimerosal ever harmed anyone, nor is there any evidence linking any vaccine or vaccines to autism. This is probably one of the most researched questions out there, and the data show time and again no link. Many studies have been conducted in recent years and none show any link between MMR or thimerosal and autism or other neurologic diseases. Expert panels have reviewed all the data and research and have all come to the same conclusion, that there is no evidence of harm or link.
Autism is a sad and difficult disease, and it is made worse by the fact that its cause or causes remain a mystery. It is also worse because the child seems normal at first and then symptoms start to appear. This leads parents, naturally, to wonder what happened to their child. This is true of other diseases, particularly neurologic diseases, that appear later in childhood. But in the absence of any evidence, it is just as logical to say that drinking milk or eating solid food causes autism as it is to say that the MMR vaccine or thimerosal causes it.
I think a certain amount of skepticism about vaccines is healthy. It always makes me a little nervous to inject my children with something. For my own children, and my patients, I always try to make sure the benefits outweigh the risks. I don’t give my children certain vaccines because I think their risk of serious illness from that particular disease is very low, so it is not worth any potential risk of the vaccine. On the other hand, I think people today have forgotten or have never seen or experienced 50,000 children every summer getting polio, with many dying or becoming paralyzed. They have never experienced parents afraid every summer of letting their children go swimming because they might get polio. The same is true of measles, mumps, and most other vaccine-preventable diseases. Even if a vaccine may have a rare side effect, in many cases it may be better than the risk of the disease itself. Still, these things ought to be investigated and if a vaccine does have a harmful side effect, efforts ought to be made to develop a safer vaccine.
So I think asking questions is good. What I find frustrating is websites and books using bad science to scare people. They literally make a scientific argument that is exactly the same as saying, “All these children who got autism also drank a substance called water. Water therefore must be causing this disease. This is just so logical.” Obviously, it is not logical at all. I believe in being cautious in the use of vaccines or any therapy for that matter, carefully weighing the risks and benefits. But I also believe in the same science that has given us hand washing to prevent death from childbirth fever, has shown that cowpox infection prevents smallpox, has given us antibiotics to kill deadly bacterial infections, safe water to drink, MRI scans and organ transplants and life-sustaining treatments for premature babies. I believe in the science that has allowed me to raise my children without fear of measles, polio, smallpox, mumps, or diphtheria. Infectious diseases were once the leading killer of children; not so anymore, thanks to many scientific factors including vaccines. I trust that same science to show whether MMR or thimerosal or anything else causes harmful side effects. I don?t believe that every vaccine is necessary for every child, and I believe that they should be thoroughly researched for effectiveness and for side effects. And right now, all the evidence says that vaccines are not linked to autism.