By Steven Novella, M.D., Yale School of Medicine
Why do people believe vaccines cause autism? Where did this myth come from? Why has it spread as truth?
In 1998, a UK physician named Andrew Wakefield published a paper in The Lancet that claimed he found a correlation between autism (a neurodevelopmental disorder), gastrointestinal disorders, and infection with the measles virus.
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The paper did not directly implicate vaccines. However, in the subsequent press conferences and media contacts Wakefield had, he specifically spread concerns about the MMR (mumps, measles, and rubella) vaccine being linked to this gastrointestinal-autism disorder connection.
The fear that vaccines cause autism spread from that point for the following decade and beyond.
Apart from the Herd
In the UK, vaccination rates with the MMR vaccine dropped from about 92 percent in 1996 down to as low as 84 percent in 2002. In some parts of London, compliance rates were as low as 61 percent in 2003. That’s a dramatic decrease in the number of people willing to take the MMR vaccine or give it to their children.
A similar thing happened shortly after that in the United States: The rates dropped, particularly in certain populations, and those populations became susceptible to previously eliminated diseases.
This is a transcript from the video series Medical Myths, Lies, and Half-Truths: What We Think We Know May Be Hurting Us. Watch it now, on Wondrium.
These rates are low enough that they’re below herd immunity. That’s the magic number of people who are vaccinated—around 90 percent—that prevents the endemic spread of infection.
This subsequently led to outbreaks of diseases that had been previously removed as endemic in the UK, such as measles.
Conflicts of Interest
Wakefield was later found to have undisclosed conflicts of interest.
Wakefield was being funded by lawyers who were engaged in lawsuits on behalf of parents who were claiming their children’s autism was caused by the MMR vaccine.
He was actually applying for a patent for a replacement measles vaccine. He was also being funded by lawyers who were engaged in lawsuits on behalf of parents who were claiming their children’s autism was caused by the MMR vaccine. Even later, there were allegations made that the data in his original Lancet paper (or some of it) may have been faked, because it didn’t square with hospital records that were then re-reviewed.
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In 2010, based on these undisclosed conflicts of interest and these allegations, The Lancet withdrew his paper from the published record. Wakefield was found guilty of professional misconduct in the UK and no longer has a license to practice medicine there.
However, the damage had already been done. Fears about a correlation between the MMR vaccine and autism were already spreading.
Thimerosal Fears
A 2010 survey found that as many as 25 percent of U.S. parents think there is a link between vaccines and autism. In that same survey, 9 in 10 parents think that vaccines are important to the health of their children. This indicates that there’s a certain amount of confusion in the general population about the safety of vaccines.
Ultimately the question of vaccine safety isn’t about the ethics or the research of one scientist; it’s about scientific evidence.
Data from Poland, the UK, Denmark, Finland, and Japan all independently found there is no connection whatsoever between MMR and autism.
There have been several studies on whether there really is a connection between the MMR vaccine and autism or other neurodevelopmental disorders. Data from Poland, the UK, Denmark, Finland, and Japan all independently found there is no connection whatsoever between MMR and autism.
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In the years following Wakefield’s paper, when the research was progressively clearing the MMR vaccine as a correlate with autism, those who were having fears about the MMR vaccine shifted to fears about thimerosal or thiomersal. Thimerosal is in some vaccines but was never in the MMR vaccine. It is a mercury-based preservative added mainly to multi-dose vials or inactivated vaccines to prevent bacterial contamination. It has been used for decades in many health and beauty products, not just vaccines.
The question is whether the ethylmercury in thimerosal is toxic to people—and specifically to children—in the doses you get from the vaccines. Mercury certainly is a neurotoxin. However, autism does not resemble mercury toxicity. They’re both neurological disorders, but the details of the signs and symptoms are different enough that we can say they’re distinct disorders.
Little Correlation
Over the last decade, there have been multiple studies in multiple countries looking at any correlation between exposure to thimerosal and the risk of developing either autism specifically or neurodevelopmental disorders in general. These studies have shown no correlation.
Most significantly, in the United States, the government decided to remove thimerosal almost completely from the routine childhood vaccine schedule. This removal was completed by the beginning of 2002.
The result: The cumulative dose children were exposed to from the entire vaccine schedule has been dramatically decreased. Those who were most vociferous about a connection between thimerosal and autism predicted autism rates would plummet after the removal of thimerosal from the vaccine program.
This did not happen.
The autism rates continue to increase at the same rate as before.
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The Danger of Medical Myths
People want and need to be able to make informed decisions about their own health care and the health care of their family. And when armed with the correct, science-based information, people can make very effective health decisions for themselves and their loved ones.
Other vaccine myths have cropped up as well.
One myth is that we don’t need to vaccinate against diseases that are no longer endemic. But the only time we can safely stop using a vaccine is when a disease is eradicated worldwide. So far, that’s only happened with smallpox.
Other people have raised fears that vaccines weaken the immune system and that natural immunity is better. However, that’s not the case. Vaccines strengthen the immune system by providing a challenge to the immune system against a very particular antigen or group of antigens.
Medical myths are not benign. They have the potential to do the most harm.
People want and need to be able to make informed decisions about their health care and the health care of their families. When armed with the correct, science-based information, people can make very effective health decisions for themselves and their loved ones.
Common Questions About Vaccines and Autism
There are many variations of autism that appear on what is known as “the spectrum.” While many factors determine whether an infant will develop autism, a complete profile of causation is not known. It is largely believed to result from inherited genetic disposition and some environmental factors such as rubella or other viral exposure.
Herd immunity occurs when a significant portion of the population is immunized so that even those without immunization are less likely to contract a disease as it can no longer spread as easily. In this situation, the disease has been contained.
Known as viral shedding, vaccine shedding is when a person releases a live virus after being vaccinated by a live vaccine. It is very rare as only a few vaccines are made from live viruses, the rest being from dead viruses or isolated proteins.
The MMR vaccine is a blend of live Measles, Mumps, and Rubella viruses that have been weakened.
