Home > Vaccine Misconceptions > Vaccine Misconception of the day-It happened after the vaccine therefore it was caused by it

Vaccine Misconception of the day-It happened after the vaccine therefore it was caused by it


As you research vaccines, you will inevitably come across stories like this one, detailing something bad happening right after vaccines were administered. Some times, right after means a few hours; other times right after means days or even weeks. Unfortunately, it is an all too human reaction to try to causally connect two events that follow each other in time. Event A happens; some time after event B happens and our natural propensity is to assume that A caused B, simply because B follows A in time. However, it behooves us to understand that it need not be so, that this is a common type of logical fallacy. When this sort of sequence of events occurs, people try to figure out what they did out of the ordinary prior to the bad event happening, and that leads to the post hoc fallacy.

To help drive this point home, think about the current egg recall in the United States. As you may know, a major egg recall is in effect due to salmonella contamination. For purposes of our exercise we will assume that you love eggs, and every morning prepare yourself an omelet. Unbeknown to you, you purchase contaminated eggs. You cook them and consume your omelet. The next day you repeat the process, but also go to check out a new restaurant that opened in your neighborhood. The third day, you consume another egg, and a short time after you become sick and the doctor tells you that you have salmonella.

If you didn’t know about the contaminated eggs, the natural propensity would be to assume that you got sick at the restaurant, not from the eggs. The same logic would be in play here: the only thing you did differently was going to the new restaurant, and you got sick right after eating at the restaurant.  The disease followed eating in the restaurant temporally, therefore it must have been caused by it, the fallacy goes. Clearly you would be wrong in your conclusion, as it was the eggs that made you sick. This is why the post hoc fallacy is a fallacy. Just because something follows something else temporally, it does not mean it was caused by it.

The same applies to vaccines. Just because a disease is diagnosed “right after” some vaccines, does not logically lead to the conclusion that it was caused by the vaccines, especially if we play fast and loose with the definition of “right after”. The only way to establish a causal relationship is through large-scale, randomized, double-blind, scientific studies examining the supposed connection between the two events. So far the evidence does not support most of these claims; vaccines have not been linked to autism.

However, vaccines are not 100% safe, just like all other medicine we use they have side effects, mostly mild, but in very rare cases severe. Overall, we must do a cost benefit analysis, as we do with everything else. The harm that is prevented through vaccines, the lives saved, the suffering avoided, hugely overshadows the harm caused by vaccines. This does not mean we should be happy and willing to live with the side effects; if they can be reduced even further we should strive for that, the same way we should strive to improve airplane technology; cars, car seats etc.

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  1. LAB
    September 10, 2010 at 11:36 AM

    It would be interesting for someone to put together a study on this. Find parents who say their child’s autism or other chronic health problem/s began “right after” a vaccine. Get the story from the parents, as they recall it. Then inspect the child’s medical records to see when and if the parents called or came in with concerns about the child, post-vaccine. Does the parent call the doctor regarding the “vaccine reaction” hours later? Days later? Weeks later? Months later? A year later? When the child immediately ran a high fever and became lethargic (as is often described by people who say their child is “vaccine damaged”), was the doctor called? Was it so concerning that the parent brought the child to the ER? Considering how often you hear this same story of “vaccine reaction,” especially in autism cases, I’d expect every last one of these kids to have a lot of detail in the medical records regarding follow-up care or serious concerns the day of the vaccine.

    I’m just always amazed by how well parents seem to recall every detail of this stuff. Would be interesting to see if their memories are reflected in the pediatrician’s records. I’m guessing no, but who knows.

    • Skepdude
      September 10, 2010 at 12:38 PM

      Oh yeah, that would be nice, and most likely would reinforce what we already know: memory is unreliable and memories morph as time goes by. Alas, that wouldn’t change anyone’s mind though. The memories, correct or not, are too vivid for the person holding them to believe they’re incorrect.

  2. September 11, 2010 at 1:04 PM

    And even if there is a correlation at one point or another, it would be expected! What folks need to understand is that in the context of the 306 million people in the United States, anomalies are actually not only expected, it would be remarkable if they didn’t occur. Here’s a back of the envelope explanation why (from another blogger that frequents BA http://padraic2112.wordpress.com/2009/04/25/my-last-vaccination-post-for-a-while/):

    There is a simple reason why this is not relevant, take the following facts:

    * children take vaccines

    * autism displays its first symptoms in childhood

    * children under the age of 5 make up ~7% of the population

    * there are ~306 million people in the U.S.

    * about 80% of children are vaccinated entirely

    This means 306 x 0.07 x .8 = 1.7 million children (roughly) have been vaccinated. With the vaccination schedule being what it is, then, there are somewhere around 100,000 children getting a shot every month (that last one is hand-wavey, it assumes a lot about frequency distributions, but that’s not really germane to my point). Autism rates are estimated at anywhere between 1 in 100 and 1 in 150 children, that means we have about 17,000 diagnosis of autism. If every single one of those autism diagnosis was given to a vaccinated child (they’re not, but again for our sake here it introduces very small error), and those 17,000 have a scatter distribution of vaccination patterns, that means not one, not dozens, not hundreds, but *thousands* of those diagnosis came within days or weeks of a vaccination: yes, this means that dozens will occur within an hour of a vaccination.

    Put those thousands of people together on a message board (and since autism is hard to deal with, a very high percentage of these family *do* bond together, like SMA sufferers or MS or cancer or any other family-impacting disease), you’ll have a few thousand people all saying to each other, “Gee… MY kid got a shot right before her symptoms started showing, too! There are thousands of us! THAT CAN’T BE A COINCIDENCE.”

    But you can see, it actually *isn’t* a coincidence… it’s exactly what we would EXPECT to happen.

    • Elaine
      November 2, 2010 at 5:07 AM

      Calculation slightly out. Actually would be 17 million children vaccinated. Which makes your argument even stronger.

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