Noemi Molnar ·

January 2, 2021

5 cognitive biases contributing to COVID-19 vaccine hesitancy

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At least 4 out of 10 people don’t want to be vaccinated. Why? Because of vaccine hesitancy, which is driven by cognitive biases.

Researchers worked tirelessly to find the ultimate way out of the pandemic: vaccination. Now that the vaccine(s) is ready and approved, our lives have the chance to turn back to normal. However, there seems to be another roadblock: vaccine hesitancy. Vaccine hesitancy refers to “delay in acceptance or refusal of vaccines despite availability of vaccination services” (ECDC, 2020, p.1). In this article we will explore the five most likely biases that can contribute to this phenomenon.

I. Omission bias

Omission bias is a preference for inaction even when taking action is substantially more beneficial.

In the context of vaccination, people tend to give disproportionate weight to harms of receiving a vaccination and dismiss harms that accrue from not receiving a vaccination – such as getting infected with COVID-19, infecting others, life not returning back to normal, or not being able to travel. Many people are concerned with the long-term consequences of the vaccines and fear that they have not been tested long enough. However, they often don’t consider (or not as much) the potential long-term negative side effects of COVID-19, even though researchers have already found many: higher chance of developing diabetes, depression, etc.

How can people’s omission bias be eliminated/counteracted?

  1. Compare risks directly, focusing separately on short-term and long-term (side) effects (e.g. vaccine’s long-term side effects vs. possible COVID-19 long-term consequences/ complications).
  2. Highlight the unique benefits of vaccination and what those who do not get vaccinated miss out on (e.g. highlight events with emotional connections such as: seeing friends/family without the fear of getting infected, having a good time while traveling, etc.).
  3. Have a public Q&A where doubts are addressed by experts and provide tangible examples from messenger channels that can influence the perception of the decision maker.

II. Availability bias


Availability bias is the human tendency to think that examples that come easily to mind are more representative than they actually are for a given population. This hampers individuals’ critical thinking and, as a result, the validity of their decisions.

In the context of vaccination, media and social circles are much more likely to bring up rare occurrences (e.g. allergic reaction to the vaccine (“2 Alaska Health Workers Got Emergency Treatment After Receiving Pfizer’s Vaccine”)). Therefore, an individual is much more likely to have these cases in mind and think that this could happen to him/her. As a result, the perception of the safety of vaccines can decrease disproportionately.

How can people’s availability bias be eliminated/counteracted?

  1. Highlight the positive changes the vaccine brought to people, give voice to individuals who received it and are happy with the results (share personal stories). Companies can encourage their employees as well by giving advocates a voice and by implying that this is the new norm.
  2. Show easy to understand statistics that highlight the general positive trend.
  3. Require media to report the cause of a side effect and to emphasize that the side effect is a rare occurrence, which specific populations can be affected by.

III. Optimism bias

Optimism bias is a cognitive bias that causes someone to believe that they are less likely to experience a negative event.

As time flies, people are getting more and more reassurance that they are not going to catch the disease, that they are part of the lucky group. This can lead to a fake optimism bias which can explain why many people are not taking precautions such as social distancing, wearing masks, or hand-sanitizing. In the context of vaccination, people can show the same confidence in their perception of not needing the vaccines due to not catching the virus or even if infected, having light symptoms. They can also underestimate the likelihood of infecting others causing harm/difficulties in their social circle, therefore they might not feel the need to get vaccinated to protect others or society as a whole.

How can people’s optimism bias be eliminated/counteracted?

  1. Continuously remind people about the risks of COVID-19 and the presence of the disease in their environment.
  2. Make it personal – highlight personal stories, show how older people have to live due to disease.
  3. Tailor the message to each generation, target group. Some examples:
    – e.g.: the younger generations are least likely to feel the need for vaccination, therefore they can be encouraged by taking responsibility for other people, such as their grandparents – ask them “who are they getting vaccinated for”.
    – Good examples of messages for healthcare workers can be found here:

IV. Confirmation bias


Confirmation bias is the tendency to search for, interpret, favor, and recall information in a way that confirms or supports one’s prior beliefs or values.

In the context of vaccination, if people believe that vaccination can be harmful, when they read the news or talk to other people, they will only focus on information which highlights real or even false evidence confirming/reassuring their original beliefs. Many people rely on others to make their decisions, such as parents, friends, doctors; therefore, people can easily take on other’s belief system and not think critically on their own.

How can people’s confirmation bias be eliminated/counteracted?

  1. Create cognitive dissonance in people – make them think about it or use humor to highlight flaws in their decision making (e.g. Jimmy Kimmel: A Message for the Anti-Vaccine Movement:
  2. Utilize social identity – show that respected identities within the group to which an individual belongs are acting contrary to their beliefs. This, in return, makes people consider the validity of their own judgments and reevaluate their choice.
  3. Make people consider the alternatives themselves, i.e. the null hypothesis.

V. Natural risk bias

Natural risk bias in the context of vaccination is when a risk of disease is more acceptable than man-made risks.

Just as we expect self-driving cars to make no mistakes at all, but watch thousands of people die due to man-caused accidents, a man-made vaccine has to meet the highest standards. Any small side-effects or negative news will probably be taken out of proportion.

How can people’s natural risk bias be eliminated/counteracted?

  1. Help people understand that (medical) experts support the current vaccines and why they should trust them.
  2. Address key concerns of the public on several occasion (e.g. vaccines cause autism in children).
  3. Highlight the success of prior vaccinations, how they made our lives safer even though we do not realize it now.

***Another psychological factor that is important to know***

As we mentioned the importance of the right messenger for specific groups, it is useful to know more about the messenger effect.

Messenger effect

We are heavily influenced by who communicates information. Some people we listen to, some we don’t, and some we question.

In the context of vaccination, people are heavily influenced by who communicates information about the safety/importance of vaccines. The question is who do people trust and turn to for advice: their doctors, researchers, government officials, family, or just their friends?

Who can be the right messenger?

  1. The country’s leaders should be one of the first to be vaccinated to show people they are confident in the vaccine(s).
  2. Doctors and other health professionals can be a reliable, expert source of information.
  3. People should be encouraged to become advocates in their social circle (e.g. “I am vaccinated” stickers, Facebook covers could be passed around).
  4. Influential people should address specific target groups.


All in all, one of the biggest challenges of 2021 is going to be gaining public acceptance of COVID-19 vaccines. Countries that can effectively and efficiently vaccinate their citizens can get back to ‘normal’ and thus recover quicker from the pandemic. Behavioural science can provide great advantage in vaccination efforts as people can be nudged towards better decisions. Some governments/companies are already utilizing behavioural science tools as we speak.

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References & Further readings

2 Alaska Health Workers Got Emergency Treatment After Receiving Pfizer’s Vaccine. (2020). Retrieved 29 December 2020, from

Brewer, N. T., Chapman, G. B., Rothman, A. J., Leask, J., & Kempe, A. (2017). Increasing Vaccination: Putting Psychological Science Into Action. Psychological Science in the Public Interest: A Journal of the American Psychological Society, 18(3), 149–207.

Browne, M., Thomson, P., Rockloff, M. J., & Pennycook, G. (2015). Going against the Herd: Psychological and Cultural Factors Underlying the “Vaccination Confidence Gap.” In PLOS ONE (Vol. 10, Issue 9, p. e0132562).

Connolly, T., & Reb, J. (2003). Omission bias in vaccination decisions: Where’s the “omission”? Where’s the “bias”? In Organizational Behavior and Human Decision Processes (Vol. 91, Issue 2, pp. 186–202).

Covello, V. T. (1988). Informing people about radiation risks: a review of obstacles to public understanding and effective risk communication (No. INIS-XN–148).

Dolan, P., Hallsworth, M., Halpern, D., King, D., & Vlaev, I. (2010). MINDSPACE: influencing behaviour for public policy. 96.

Klayman, J. (1995). Varieties of Confirmation Bias. In J. Busemeyer, R. Hastie, & D. L. Medin (Eds.), Psychology of Learning and Motivation (Vol. 32, pp. 385–418). Academic Press.

Long-term effects of COVID-19. (2020). Retrieved 29 December 2020, from

Sharot, T. (2011). The optimism bias. Current Biology: CB, 21(23), R941–R945.

Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology, 5(2), 207–232.

Vaccine hesitancy. (2020). Retrieved 29 December 2020, from

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