Why are people so sure about the connection between vaccines and autism?
Anti-vaxxers are a small but vocal group that disagrees with the general scientific consensus that vaccines are safe and do not cause autism.
Most in this camp don't care that more than a dozen studies have stalled in their search for a possible link between the two phenomena. How can this be? How can people deny scientific evidence? It's all about the so-called Dunning-Kruger effect, a cognitive bias that explains anti-vaccine sentiment. The Dunning–Kruger effect, proposed by David Dunning and Justin Kruger in 1999, describes a situation in which people who have very little information about a topic believe that they know much more than experts. One of the founders of the concept of this effect, David Dunning, explained it this way: “The area of people's ignorance is often invisible to them.”
In 2021, a team of researchers led by Dr. Matt Mott of the Annenberg Public Policy Center at the University of Pennsylvania conducted a survey and found that people who knew little about autism, lacked knowledge of basic facts, and tended to believe misinformation believed they knew more than experts. This self-confidence leads some to not support mandatory vaccination policies and to express skepticism towards doctors.
1310 people took part in the survey. Dr. Mott's team found that 36% of respondents believed they knew more than doctors, and 34% said they were aware of the possible causes of autism. The greatest degree of overconfidence was observed among those who had the least level of knowledge and the highest tendencies to maintain misinformation. These same people showed a predisposition to support non-experts - like various celebrities - involved in policy development.
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Many people believe that anti-vaccine sentiment is harmless, but scientific studies like the one described above show that it has an impact in the real world. Thus, communities that resist vaccination are steadily increasing. And it is not surprising that they are the ones at greatest risk of contracting the viruses against which they refuse to be vaccinated. It’s even worth remembering the measles outbreak at the end of 2021 - beginning of 2021.
In 2021, Dr. Peter Hotez of the National School of Tropical Medicine at Baylor College of Medicine conducted a study in which researchers found an increase in the number of exemptions from vaccination for non-medical reasons in 12 of the 18 states that allow the practice.
“In recent years, the anti-vaccination social movement has been growing in the United States; as a result, measles outbreaks have become more frequent,” Hotez and his colleagues said at the time.
Back in mid-2018, Hotez's research team noted that increased opposition to vaccination would also lead to more disease outbreaks.
However, anti-vaxxer communities continue to grow and repeat, like a mantra or mantra, that vaccines cause autism.
What is DPT vaccination?
DTP (adsorbed pertussis-diphtheria-tetanus vaccine) is considered today one of the most “scandalous”, since a “cocktail” of three serious diseases is introduced into the child’s body: tetanus, diphtheria, whooping cough.
DTP vaccinations are done all over the world, and they contain a viral part (the so-called antigen) and preservatives (they prevent the development of microbes in the vaccine and extend its shelf life).
2015 Study and Breaking Ground
In 2015, an article appeared in the Journal of the American Medical Association about a large-scale study at that time, the purpose of which was to confirm or refute the connection of the MMR vaccine (combined measles, mumps and rubella vaccine) with the occurrence of autism (the study report itself can be found link.
The work, conducted by Dr. Anjali Jain and her colleagues, looked at the medical records of 95 thousand children, including 15 thousand unvaccinated children aged two to five years, as well as about two thousand children already at high risk of developing autism.
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Consistent with previous similar studies, the researchers found no association between the MMR vaccine and the risk of developing autism spectrum disorder (ASD). This turned out to apply to almost two thousand children at high risk of developing autism.
“Consistent with studies of other populations, we did not observe an association between MMR vaccine and increased risk of ASD,” the authors wrote. “We also found no evidence that receiving one or two doses of the MMR vaccine was associated with an increased risk of ASD among children who have older siblings with ASD.”
The analysis examined rates of autism and the MMR vaccine among children aged two to five years. Researchers have not identified an increased risk of developing autism due to immunization at any of these ages. Moreover, there were fewer cases of autism among the vaccinated groups. But, as the scientists noted, this may be due to the fact that parents, having noticed early signs of autism, could postpone vaccination or refuse it altogether.
It is important to note that there have been studies over the years that have attempted to establish a causal relationship between the MMR vaccine and autism. Each time the samples grew larger, but no connection was established. In 1998, the Lancet published a study conducted by Dr. Andrew Wakefield and his colleagues, which stated the opposite: there is a direct link between vaccinations and autism (the work can be found here.
This study has now been refuted and retracted from the journal. If you follow the link, in the background of the text you will notice a large inscription in red letters: “RETRACTED”. It is not surprising that such a high-profile article aroused interest among other specialists, and they, in turn, decided to conduct their own research. As already mentioned, confirmation of the described data could not be found. However, the speculation surrounding this issue to this day has left many people uneasy. Many people fall victim to the Dunning-Kruger effect. It could also be that these worries are responsible for the decline in vaccination rates among families with an older child with autism—at least that's what the authors of a 2015 study suggested. Following Dr. Wakefield's article, many other articles that suggested a link between vaccination and autism were retracted.
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However, in 2015, Dr. Jain's work showed that among families without children with autism, 84% of children aged two and over and 92% of children under five were vaccinated. In families where the eldest child had autism, vaccination rates were significantly lower: 73% of children over two years of age and 86% of children under five years of age.
Reviews from parents
The Internet is flooded with forums where parents discuss the causes of autism in their children. Some of them claim that regressive autism develops from the DTP vaccine . Since it is not possible to confirm or refute these statements, we will simply provide a brief overview here.
- There is a group of parents who believe that their child had signs of autism even before vaccinations. Since these children were the first-born, the parents did not know how the child should develop correctly. Such reviews are typical for families where the second child is healthy and now there is something to compare the development and behavior of a child with autism and a healthy one.
- The second group is parents of children with regressive autism, which is diagnosed after 2-4 years. These parents directly link autism and vaccinations, since before vaccination the baby’s development corresponded to the age norm. Those who noticed autism in a child from vaccinations more than anyone else. However, this can be explained by the presence of problems and the search for a way out.
- The third group believes that vaccinations have become a “trigger mechanism”, and autism itself is in the genes.
All parents agree on one thing - until the cause and mechanism of development of autism is clarified, it is not possible to say anything unambiguously.
Danish study 2021 – a new frontier
In the United States, measles was eliminated in 2000. In 2010, the World Health Organization approved a strategy for the global elimination of measles by 2015. It was ambitious and, as it seemed, quite feasible.
By the beginning of 2019, 206 cases of measles were reported in 11 states in the United States. Between January and December 2021, 82,596 cases of measles were reported across the EU. The return of the disease is directly related to parents who increasingly refused to vaccinate their children with the MMR vaccine. This, of course, does not play into the hands of parents who have vaccinated their children in an attempt to protect them from such contagious diseases as measles, rubella and mumps. The anti-vaxxer movement as a whole is based on Dr. Wakefield's research, which was already mentioned above. It was he who first linked vaccinations with the increasing number of cases of autism in children. Although his research was refuted by 2010, widespread confidence in Wakefield's claims has proven incredibly resilient.
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On March 5th of this year, the most recent study on this issue was published in the Annals of Internal Medicine. It is based on data collected over ten years from half a million people. However, we note that, despite the unprecedentedly large sample, anti-vaxxers, driven largely by paranoia, shifting blame to others, distrust of specialists and even just stubbornness, are unlikely to consider this significant evidence to refute their beliefs.
The study was conducted by scientists from the Statens Serum Institute in Denmark. It found no statistical connection between receiving a vaccine and the possible development of autism (the work is available here. Also, no connection was established between the areas in which vaccines are used and those in which the development of autism is associated. Moreover, with the growth of the anti-vaccine community Cases of autism have also become more frequent: in 2021, autism was observed in one eight-year-old child out of 68 children, and in 2018 – in one out of 59.
The researchers examined the medical records of Danish children born between 1999 and 2010. Using a population registry, the researchers assessed other risk factors, including autism among siblings, as in the 2015 study, and scrutinized the suspected relationship between vaccination and autism. Discussing the statistics presented in the study, health expert Saad Omer told the Washington Post, "The correct interpretation is that there is no connection at all."
However, the same Omer and a number of other experts believe that, despite all the evidence presented in the Danish study, spending research money on convincing anti-vaxxers is a dubious idea. Bioethicist Sid M. Johnson commented: “They are immune to facts.” Almost simultaneously with the study, Omer published an editorial in the Annals of Internal Medicine decrying the waste of time, effort and money on people living in a “fact-resistant” world.
Omer and other experts worry that anti-vaxxer beliefs are undermining public trust in vaccines, and say the expense of gathering evidence to the contrary is only justified if the cost of such research is not too high. He also noted that this money could be spent in an alternative way, namely on drug development.
The publication of this study coincided almost perfectly with a US Senate hearing in which 18-year-old Ethan Lindenberger testified about his decision to get vaccinated against his parents' wishes. Lindenberger previously wrote on Reddit that after reading Facebook posts, his mother became convinced that vaccines were “some kind of government scheme.” In his post he writes: “I’m booked in to get my shots in a few weeks! My mom was very angry, but my dad said that since I was already 18, he didn’t really care. Even though my mom tries to convince me not to do it and says I don’t care about her, I know I just have to do it no matter what.”
In turn, Facebook said it is taking the necessary steps to limit the spread of health-related misinformation. Already on March 6, the company announced a new plan in which all advertising posts containing false information regarding vaccines would be blocked, and over time the advertising accounts of pages that continue to violate the network's rules would be blocked.
Possible consequences of DTP
Immunization involves placing a lot of stress on the body and immune system. Even modern medicine has not yet managed to create drugs and vaccines that would be “indifferent” to our body.
DPT vaccination for a baby is difficult, and after vaccination the following symptoms may be observed for the first 3 days:
- increase in rectal temperature from 37 to 40 degrees;
- irritability;
- redness, swelling (diameter up to 8 millimeters) and pain in the grafting area;
- lack of appetite;
- drowsiness;
- diarrhea;
- vomit.
The symptoms described are standard and should not cause any panic among parents.
Parents should be alert to the following reactions:
- convulsions;
- elevated temperature for more than 3 days;
- compactions at the vaccination site;
- Quincke's edema.
Important: keep in touch with your pediatrician after vaccination.
