Vaccine Fallacy

The fear of vaccines is based on fear of needles and a simple logical error that the ancient Romans called post hoc, ergo propter hoc. It is a way of erroneously leaping to conclusions. You presume that because B happened after A, A must have caused B. Here are some examples of similar errors:

Logical Fallacies
Conclusion What You Are Ignoring
You step on a crack. You ask as your mom how her back is feeling. She says it hurts. You conclude you broke her back. Lots of people step on cracks every day, and nothing happens to their moms. Your mom always complains about her back when you ask, whether you have stepped on a crack or not.
Both your grandmothers asked for a glass of water shortly before their heart attacks. You conclude that drinking water causes heart attacks. Your grandmothers drank thousands of glasses of water in their lives without ill effect. The oncoming heart attack was making them feel uncomfortable and they thought a glass of water might help.
You bought a new Volvo and took your girlfriend on a picnic. The next day she dumped you. You concluded that riding in Volvos make women lose their attraction for you. Lots of other people own Volvos, and their partners do not leave them. Are you ignoring the way you said she was a fat cow at the picnic?
You heard on the Internet about someone whose son started showing symptoms of autism shortly after getting a vaccine. You conclude the vaccine (type unspecified) caused the autism. The most important thing you ignored is almost all babies get immunised. Very few of them develop autism. Even if vaccines have nothing to do with autism, it would be very hard to find an autistic baby who had not had a shot. This is almost as silly as blaming autism on milk since almost every baby who developed autism had prior exposure to milk. You trusted an anonymous, uncredentialed source to get the details right, and not to lie to you. They obviously had an emotional agenda. You ignored that bias. Autism is probably genetic. You ignored that the baby in the anecdote probably had autism from birth, but the condition did not reveal itself until vaccination age. You ignored the fact your conclusion is based on only one sloppily researched anecdote whereas the science is based on the results from observing millions of children in many different countries. The vaccine in question may have been a known dangerous vaccine such as rabies or Ebola, and you are projecting its dangers on a safe vaccine like measles. Your error has consequences. Every vaccination you discourage means increased risk that some child, not necessarily your own, is going to get sick and perhaps die. Cranks who pontificate against vaccines generally have no idea how serious the diseases are the vaccines prevent. Measles, for example, sometimes kills or causes brain damage. I consider cranks who spread false information about vaccines as attempted murderers.
~ Roedy (1948-02-04 age:70)