She was a 51 year-old lady with asthma so severe that she required regular injections of a special medicine to keep her out of the hospital. She had prolonged damage to her lungs from her disease and daily symptoms of wheezing and shortness of breath. Any insult, whether it be a cold or cut grass, could put her out of commission. So when I asked her if she had her COVID vaccine she surprised me when she said was afraid of the side effects. So, a woman who has a very high likelihood of dying from this virus, was afraid of the vaccine. Her fear was driven by reports of scary side effects, most recently with the Johnson and Johnson vaccine.

Her decision was irrational but predictably so.

There is an area of psychology dedicated to the study of how our brains have specific and consistent errors in judgment that make it hard for us to make rational decisions (to do your own deep dive read Thinking Fast and Slow by Daniel Kahneman). This area of psychology focuses on the regular and systematic mistakes we make with alarming frequency and consistency. The problem with almost all of these mistakes is that we are completely unaware of them. Nobody is immune. We are irrational in a very predictable way.

Some of these errors are called heuristics. This is a fancy term for mental shortcuts that allow us to make decisions more rapidly and easily. With heuristics our brains substitute an easier question for a harder one. For example, if someone asks you how much you want to donate to save the endangered white rhino you will substitute the answer to the question, “how do I feel when I think about endangered rhinos?”. You don’t do a complicated budget analysis to determine how much money you have available to donate to charity and how you want to divide that money up. Going with your gut is easier and works a lot of the time. But not all the time.

We are irrational in a very predictable way.

It’s a bit complicated, but in our current time, one of these heuristics has been called the availability heuristic. To avoid overcomplication, think of this as an error in judgment that causes us to overestimate the risks of things that are more easily brought to mind. So if something is very dramatic, scary, or emotional, it will come to mind more easily and we will judge it to be more likely to occur than it actually is.

An example of how this works is the common fear of flying relative to the fear of driving. The risk of something bad happening in an airplane is many times less than in the risk of something bad happening in a car but more people are afraid of flying than driving. The availability heuristic is the reason. When a plane crashes it is all over the news for days (if not weeks) with images brought to mind of many people die in a dramatic and horrific fashion. This creates a very salient and powerful emotion-inducing image. When we consider flying in a plane we are, whether we realize it or not, estimating the risk of that horrible image happening. These dramatic images cause us to overestimate the likelihood of a crash and trigger fear. Driving is something we do every day and the crashes “only” kill a few at a time and do not dominate the news cycle. Car accidents do not induce the same emotional response so we underestimate the risk of a crash even though it is orders of magnitude more likely than a plane crash.

With this in mind, recent reports of blood clots in the brains of 6 individuals who received the Johnson and Johnson vaccine have dominated the news cycle. The reports are vivid and quite frightening and have prompted a pause on the use of this vaccine. There were also reports of blood clots associated with the Aztra Zeneca vaccine, also in a very small number of individuals.

This creates the following scenario. An individual has to decide whether or not to get a vaccine. This decision is really a weighing of risk. What’s the risk of a bad side effect from the vaccine vs the risk of something bad happening from not getting the vaccine (i.e. from getting COVID). People will not generally calculate the actual risk and make a rational decision based on the calculation, they will instead react to how scared they feel by the two outcomes even though they have very different likelihoods. Because of this heuristic, the vividness and dramatic nature of the news reports will cause people to greatly overestimate the risks of the vaccine and underestimate the risks of not getting the vaccine.

But what are the actual risks?

For the Johnson and Johnson vaccine there were events in six women between the ages of 18 and 48 years old . There have been about 7 million total doses of the vaccine given in the United States as of right now. For simplicity, let’s call the overall risk of these clots to be 1 per million. For comparison, the death rate from COVID-19 in the same age group is 125 per million. And that’s with deaths from the clots. Of the 6 who got the rare clots, only one has died and one is in critical condition. This means the risk of dying from COVID 19 is several hundred times greater than the risk of dying from a brain clot. This will be true even if several hundred more cases are discovered.

the risk of dying from COVID 19 is several hundred times greater than the risk of dying from a brain clot.

The pause is concerning for many reasons and I worry it will create a scenario where the cure is worse than the disease. Delaying getting vaccines to the public delays the time to full vaccination. This is all happening as case rates are steadily rising from the UK variant spreading throughout the continent. It also adds to vaccine hesitancy which will slow vaccine uptake and delay the time it takes for us to reach herd immunity.

The pause by the FDA is to raise awareness of the potential side effect to see if it is more widespread than currently reported. This is unlikely and it shouldn’t take long to find this out. Unfortunately, the damage caused to public trust and by delays in vaccine delivery will be much more long lasting but you can help prevent that from happening. All you have to do is avoid becoming a victim to your heuristics and get your vaccine. Even if there are risks to the vaccines, the risk are small and it’s far more likely that something bad will happen to you if you don’t get the vaccine than if you do. After you’ve overcome your heuristic roadblock and been vaccinated help your friends and family get over theirs and get their shots. Getting to herd immunity is a team effort and we can all play a part. We’re almost there…

13 thoughts on “Why the Johnson and Johnson vaccine side effect is so worrisome

  1. Dr. Grove:

    Thank you for your post. I want to point out what I feel is a relevant point that is not being considered here.

    The choices that you are comparing are assuming that it is inevitable that everyone will get Covid- there is no stopping it. So, under that assumption, yes- not getting the vaccine is silly, according to Michael Gerson in today’s Washington Post, a free-rider.

    I think the comparison needs to be between taking the vaccine and not taking the vaccine and avoiding sugar, eating healthily, getting sleep, keeping your body and lungs in tip-top shape, and wearing masks until the pandemic goes away.

    I think that it is reasonable to pick the latter, and not the former.


      1. The young in good health are not masking in my experience.

        Until September, the official pronouncements were that with masking and social distancing we can beat Covid. As it became clear that a vaccine is on the horizon, the messaging switched to “vaccine” is the elixir. The messaging changed probably because people decided that living with a mask is not worth it.


      2. Your premise and facts are not correct. No expert said we could “beat COVID” (maybe a politician or news outlet did). The plan was to flatten the curve and mitigate spread with masking, distancing, etc. The vaccine is the only thing that will end the pandemic.


      3. Dr. Grove-

        It seems that you are saying that the only way to eliminate Covid is with the vaccine. Am I understanding you correctly? If yes, then how did the pandemic of 1918-1920 subside?


      4. The only way to eliminate the pandemic without millions and millions more dying and destruction of our healthcare system is with vaccination. The Spanish flu ended with untold devastaion and there was no healthcare system. Also, coronavirus behaves very differently epidemiologically with less seasonality so that it doesn’t “burn out” the way flu does.


  2. Thank you for continuing to educate us.
    Please consider that you may be guilty of creating the exact availability heuristic you are talking about with your “hook”/ sensational headlines. Many people glance at the title of a post and assume the conclusion with out reading through.


  3. Dear Dr. Grove,
    Thanks for providing such level-headed, clear information throughout the pandemic!
    In my part of town, there is a large resistance to getting vaccinated. The claim is a lack of information on the long term effects of the various vaccines. How do you address this?
    Please accept my fully vaccinated thanks for all your efforts since the very beginning of this interesting chapter of our lives!


    1. I would say that it is not clear what the long term effects of getting COVID are either. Either way there is great uncertainty. The overall chances of something bad happening to you, whether in the short or long term is clearly higher without the vaccine than with.


  4. Saying the long-term effects are not clear, then saying the overall chances are better, are two contradictory statements. Much of the reasons we have the problems we do are due to people not being taught to think for themselves, actually miseducated and encouraged not to think for themselves, making that popular, and as such, they become easily manipulated to not follow lines of reason, principle, and cause and effect results. Even when I explain anything to someone, I encourage them not to agree with anything I say, but only if what I say coincides with their own understanding, perhaps requiring research. If someone agrees with me blindly, I don’t want them following me, because they to learn responsibility for whatever decisions they make.


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