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Vaccine hesitancy and how nudge can increase their uptake

Updated: May 24, 2021

On December 2019, the SARS-CoV-2 virus was first identified in the city of Wuhan and rapidly spread around the world, causing a global pandemic. So far, this virus has infected over 119 million people and killed 2.6 million across the world (Dong, Du & Gardner, 2020). One year later, the first vaccines against Covid-19 became available and vaccination programs were developed across countries. However, vaccines are only useful if there is a wide number of people who are willing to be vaccinated. Otherwise, public health issues may occur. What is happening is that many people are reluctant towards being vaccinated, what can be referred to as vaccine hesitancy, i.e., delay in acceptance or refusal of vaccines, despite availability of vaccine service (WHO, 2020). Although this is a complex phenomenon, there is an inherent cognitive component of special importance, which is the role that cognitive biases play in our judgments and decision-making processes.

Cognitive biases:

We tend to think that negative outcomes are more likely to happen to others, while positive ones are more likely to happen to us. This is called optimism bias (Weinstein, 1980). Therefore, people who haven’t been infected yet with SARS-CoV-2 virus or even people who only had light symptoms of the disease, might minimize the importance of vaccine immunization.

Most of the time, on communication channels and social media, information about rare events, such as a specific person who developed side effects or allergic reactions to the vaccine, is more likely to be spread. This can make those events easier to remember and lead us to a false overestimation of its occurrence, making us rely on a mental shortcut known as availability heuristic (Tversky & Kahneman, 1974), making us believe it is highly likely that the same will happen to us, if we get vaccinated. Moreover, people are healthy when they get vaccinated, so the fact that it can cause side effects also contributes to vaccine hesitancy. Research shows that we tend to opt for the risks associated with not taking an action (e.g. possibility of contracting Covid-19) more than to opt for the risks that come from an action (e.g. get vaccinated) even if it is better for us. This is known as omission bias (Dubé, Laberge, Guay, Bramadat, Roy & Bettinger, 2013), which is related to the naturalness bias: our inherent tendency to prefer and perceive as less risky what is natural, compared to what is artificially produced by humans (Dibonaventura, & Chapman, 2008), leading us to perceive risks associated with the disease as more acceptable than those caused by vaccines.

How can nudge help to increase vaccine uptake?

Getting people to schedule an appointment can be difficult and it can create some problems in this particular case of Covid-19 vaccine because it requires two shots, within an interval of at least, 21 days. So, one way to nudge people is to schedule the appointment for them. Research shows that flu vaccination increased by 36% when people were given a time, date and location to get the vaccine. This works as an opt-out system that requires effort from people to change their appointment which, usually, makes them stick with the default option (Chapman, Li, Colby & Yoon, 2010).

All the campaigns and messages spreading around the globe about vaccination can be more effective through framing effects. Simple changes in the words used for identical problems can alter people’s decisions, such as describing an outcome in terms of losses versus gains. We have a predisposition for experiencing losses as more devastating than to be gratified by equivalent gains, which is known as loss aversion (Tversky & Kahneman, 1981). Thus, campaigns to promote and increase vaccination should be framed in terms of what people lose if they don’t get vaccinated, instead of what they gain from being vaccinated.

Vaccination is the most effective method to combat Covid-19 pandemic and to ensure public health in the world. Therefore it’s crucial to make people carry the conviction about the importance of vaccination and that policy makers work towards this goal using the insights and knowledge from behavioral sciences.


Mariana Marques



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Dong, E., Du, H., & Gardner, L. (2020). An interactive web-based dashboard to track COVID-19 in real time. The Lancet infectious diseases, 20(5), 533-534.

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WHO. (2020). Vaccine Hesitancy: what it means and what we need to know in order to tackle it [Online]. Available at:

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