The Centuries Old Vaccination Debate
The 'vaccination debate' is as old as the introduction of the first vaccinations in the eighteenth century. A minority of anti vaccinationists rejected vaccinations with 4 main arguments, which have stayed remarkably the same over the centuries: 1) vaccinations cause all kinds of harm (syphilis, measles, encephalitis, autism, death, et cetera, depending on the time period); 2) vaccinations are unnatural; 3) vaccinations are against God's predestination; 4) vaccinations are forced upon us by Edward Jenner/the pharmaceutical industry to earn profit.
Unfortunately, in the twentyfirst century anti vaccinationists are winning ground and vaccination rates are dropping. This causes a global public health risk. The anti-vaccination lobby would not be so successful if more people had a better grasp of vaccination history, basic causality, communication science and statistics. As a historian, a data scientist and a father I will argue why the idea that vaccinations cause all kinds of bad side effects, most notably autism, is a dangerous myth. If you are convinced vaccinations cause harm I do not have much faith in changing your mind, even if you are still reading, unless you keep an open mind. This blog is mostly for people who are in doubt, or are not sure what to think. Or for people who are not in doubt but want to use more solid arguments against anti vaccinationists. I will demonstrate that even though it is very understandable people still think vaccinations cause harm, there is no basis in facts or logic to do so.
Echo Chambers and Confirmation Bias
In this century the vaccination debate has found its way to online communities, where it has been carried on with increased intensity. Despite irrefutable scientific evidence to the contrary, an alarming number of people are convinced that vaccinations cause autism or other unwanted side effects. This at least has partly to do with the online world facilitating the easy creation of new 'echo chambers'. Echo chambers are sealed off (metaphorical) spaces in which like minded people find each other and confirm each other in their beliefs. In earlier times echo chambers were mostly formed in small communities, but in the online world they can integrate people from all over the world. The internet also facilitates the availability of all kinds of information. It is human to read and believe the information that confirms what you already know, even if it is contradicted by many more, and better substantiated, sources. When people lock themselves up in Echo Chambers where one sided information is spread among like minded individuals it even can seem as if the majority of the population think like they do. Any information that says the contrary can likewise be easily dismissed.
The Outliers have more impact on public perception
It is highly unlikely, yet still possible, that a vaccination causes an unwanted side effect. Still, stories of the failures are the ones that spread rapidly. You rarely hear someone saying a vaccination went perfectly, for the simple reason that it is not really something special to report. If something, supposedly, goes wrong people are far more likely to share their story. This is why the outliers, the results that are most unlike regular results, have more impact. If 1 in 10.000 vaccinations have some kind of bad side effect this potentially has much more influence on public perception than the 9.999 vaccinations that went just fine. Already in the nineteenth century anti vaccinationists often had a few horror stories ready to scare parents into not vaccinating. Since the (online) world is a big place the number of scary experiences can go up quickly, even if relatively speaking the number is still small and insignificant. A case file of a hundred 'horror stories' can serve as a scary deterrent for young parents to vaccinate.
Sometimes we have to accept we do not know or can not influence the cause
Something else which is human, is the compulsive need to understand the world and to be able to influence what is going on. In earlier centuries when a harvest failed it was the work of the devil, or a witch, or a punishment from God. You could try to improve your fate by burning the witch or by praying. A simple 'bad luck' with the weather conditions is more difficult to accept, since you cannot do much about that as an individual. No one likes to be a helpless victim of 'dumb bad luck'. Still, sometimes we have to accept this.
Just because B follows A does not mean A caused B
The difficulty to accept being helpless also is part of the reason that the link between vaccinations and autism is so persistent. It is unknown why one child is autistic and the other is not, except that it seems to have something to do with genetics. Vaccinations are scary, because it is difficult to understand what you are really injecting into your child. If your child also becomes 'visibly autistic' around age two, shortly after it received its second MMR vaccination, it is natural to think of a causal relation between something scary and something inexplicable. Human instincts are still very 'medieval'. For inexplicable phenomena people look for unlikely causes to channel their feelings of fear and helplessness. This feeling can be stronger than solid evidence that there is no causal relation between autism and vaccinations, and the exposure of the first scientist who made this claim as a fraud. 
Within a mass of big data there are no regular patterns
It also is important to realise that data do not follow any regular patterns. Statistics quickly can seem false if your own perceptions show a completely different pattern. Imagine that according to statistics 1 in 1000 children gets a high fever after being vaccinated, but that in your near surroundings you already know three children who were struck with high fevers. It is easy to think that the numbers should be 1 in 10 instead of 1 in 1000. The study must be flawed or maybe the government has made it up! It would however be extremely unlikely, even if all the other circumstances were the same, that a statistical pattern is regular. Voor many professors this knowledge even is a way to quickly spot badly falsified data. A normal pattern is not A, B, C, D, E, A, B, C, D, E, but the more random A, A, A, C, E, A, A, B, A. Results clump together, which is why many gamblers can think they are in a 'winning streak'. It however is not a winning streak, but a normal result within the advertised odds of winning or losing. Every gamble has the same chance of success, regardless of the gambler having won or lost ten times before the current gamble.
Measuring more does not mean there is more than before
It does not help that autism seems to be a modern phenomenon. People therefore try to blame modern vaccinations and changes in the environment or even food patterns. It is true that an increasing number of people are diagnosed with autism. This does not (necessarily) mean more people are autistic than before. The 'elf children', 'eccentric uncles' or 'siblings in the lunatic asylum' from centuries gone by would now get a diagnosis of an Autism Spectrum Disorder (ASD). Over the past decades, the definition of autism also has been extended to include many more variations than before. To give one extreme example: not so long ago doctors could claim that only boys were autistic. Obviously the number of diagnoses will go up when you start including the other half of the earth's population as possible candidates as well. It also is more difficult for people on the spectrum to go 'unnoticed'. Modern society likes to measure, quantify and categorise everything. Furthermore, and far more damaging, modern society subjects people to many difficult-to-channel impulses. One may wonder if brilliant minds of the past who may have been on the spectrum, like Mozart, Darwin and Einstein, could have flourished in the 21st century like they did in their own time.
Even if all of this was not true, and vaccinations indeed cause autism, why would any parent prefer to have a child die from measles or polio over having an autistic child?
 D. Porter and R. Porter. 1998. The politics of prevention: anti-vaccinationism and public health in nineteenth century England. Medical History, 32:231–252; C. E. Daniels. 1875. De kinderpokinenting in Nederland: meerendeels naar onuitgegeven bescheiden bew- erkt: eene medisch-historische studie. Amsterdam.; W. Rutten. 1997. De vreselijkste aller harpijen. Pokkenepidemieen en pokkenbestrijding in Nederland in de 18e en 19e eeuw. Universiteit Wageningen.
[2 I thank my basic understanding of statistics to Statistic Reasoning for Everyday Life by Bennett, Briggs and Triola.
 Ana Lucia Schmidt, Fabiana Zollo Antonio Scala, Cornelia Betsch, and Walter Quattrociocchi. 2018. Polarization of the vaccination debate on Facebook. Vaccine, 36:3606–3612
T. Chamorro-Premuzic. 13 May 2014. How the web distorts reality and impairs our judgement skills. The Guardian; M. del Vicario, G. Vivaldo, A. Bessi, F. Zollo, A. Scala, G. Caldarelli, and W. Quattrociocchi. 2016. Echo chambers: Emotional contagion and group polarization on Facebook. SCIENTIFIC REPORTS, 6, 37825