Study: Vaccine Skepticism May Be Caused by Cognitive or Affective Differences


Vaccine skepticism, or a hesitancy or unwillingness to get vaccinated or to vaccinate one’s children, may be the result of some people overestimating the likelihood of negative events.

Despite the measles having been eliminated in the United States in 2000, new cases of measles arose in 2019. There were 1282 confirmed cases in 31 states that year, with nearly three-fourths connected to outbreaks in New York, according to the CDC. These cases were caused by an increase in individuals deciding not to get vaccinated against the measles.1

Vaccine skepticism, or a hesitancy or unwillingness to get vaccinated or to vaccinate one’s children, emerged as a topic of interest due to its spread in certain communities in the country. As it became a more widespread occurrence, 2 researchers at the Texas Tech University Department of Psychological Sciences began to search for a possible explanation.1

In a recent study published in Vaccine, the authors suggest that some people find vaccines risky because they overestimate the likelihood of negative events, especially those that are rare.1

These overestimations apply to areas beyond vaccines and include all kinds of negative events, suggesting that people higher in vaccine skepticism actually may process information differently than those lower in vaccine skepticism, said Tyler Davis, PhD, associate professor of experimental psychology, and director of the Caprock FMRI Laboratory, in a press release.2

“We might have assumed that people who are high in vaccine skepticism would have overestimated the likelihood of negative vaccine-related events, but it is more surprising that this is true for negative, mortality-related events as a broader category,” Davis said, in a prepared statement. “Here we saw an overestimation of rare events for things that don't have anything to do with vaccination. This suggests that there are basic cognitive or affective variables that influence vaccine skepticism.”2

In the first experiment, Davis and Mark LaCour, a doctoral student in psychological sciences, surveyed 158 participants on their level of skepticism around perceived dangers, feelings of powerlessness, disillusionment, and trust in authorities regarding vaccines. Davis and LaCour then asked participants to estimate the frequency of death associated with 40 different causes, ranging from cancers, animal bites, and childbirth to fireworks, flooding, and car accidents.1

The researchers found that those participants higher in vaccine skepticism were more inaccurate in their estimations of the frequency of each of the causes of death, specifically in relation to overestimating the occurrence of rare events.1

For the second experiment, the researchers followed the same procedures as the first, but also asked participants to estimate the frequency of neutral or positive events. Including this additional element was meant to assess whether the negative tone of mortality statistics played a role in influencing participants’ decisions. Examples of neutral or positive events included in the test were the occurrence of papal visits to the United States, triplet births, or Willie Nelson concerts.1

The results of the study showed that people higher in vaccine skepticism overestimated the negative events more than the neutral or positive events, and were less accurate in their estimations of other mortality-related events.1

“My takeaway is that vaccine skeptics probably don't have the best understanding of how likely or probable different events are,” said LaCour, in a press release. “They might be more easily swayed by anecdotal horror stories. For example, your child can have a seizure from getting vaccinated. It's extremely rare, but it is within the realm of possibility. If you were so inclined, you could follow Facebook groups that publicize extremely rare events. These cognitive distortions of anecdotes into trends are probably exacerbated by decisions to subscribe to statistically non-representative information sources.”2

The researchers did not find a connection between education level and vaccine skepticism, but they were able to conclude that there is a difference in the information being sought by people higher in vaccine skepticism. This may be either due to these individuals seeking information that matches their biases or due to an attentional bias to negative, mortality-related events. Such an attentional bias would allow these individuals to remember the negative information more readily.1

“Do some people encode scary stories—for instance, hearing about a child that has a seizure after getting vaccinated—more strongly than others and then consequently remember these anecdotes more easily?” LaCour said in a press release. “Do they instead have certain attitudes and search their memory harder for evidence to support this belief? Is it a bit of both?”2

LaCour explained that the many questions the results of the study raised can lead to new avenues for further research.2

“I'm excited that we're finding basic, cognitive factors that are linked with vaccine skepticism: It could end up being a way of reaching this diverse group,” LaCour said.2


  • LaCour M, Davis T. Vaccine skepticism reflects basic cognitive differences in mortality-related event frequency estimation. Vaccine, 2020; doi: 10.1016/j.vaccine.2020.02.052.
  • Vaccine skeptics actually think differently than other people [news release]. ScienceDaily; 2020. Accessed April 13, 2020.

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