Mapping the Cognitive Biases Related to Vaccination: A Scoping Review of the Literature

"Human behavior and understanding of the vaccine ecosystem play a critical role in the vaccination decision-making process."

People experience a variety of biases, and these biases have an effect on our thoughts, behaviour, and decision-making. Cognitive biases are systemic errors in that individual's style of thinking. Biases cause people to avoid information that can be upsetting or challenging rather than looking into the facts to help make better-informed decisions. The objective of this study was to understand different cognitive biases that may lead to vaccine acceptance or hesitancy. As part of the review, the authors provide a practical categorisation scheme to assist with organising the diverse range of cognitive bias concepts. They evaluate the impact of cognitive bias on knowledge of vaccine dynamics and vaccination coverage, making suggestions for responding to cognitive bias and mitigating it.

The eligibility criteria for this scoping review was vaccination-related cognitive bias studies published in the English language from inception to April 2022 and available on PubMed, Embase, and Google Scholar. It included all geographical locations and individuals of all age groups. Fifty-eight articles were identified, and after screening, 19 were included in this study.

Overall, 24 cognitive biases were found to be have the potential to affect the vaccination process. These biases were grouped into three broad categories:

1. Cognitive biases seen while processing vaccine-related information

• The framing effect is the phenomenon wherein an individual's decision is influenced by the presentation of communication content without changing its main message.
• Base rate neglect is the tendency to focus on specific information while disregarding general information, even when the general information may be more important. An instance of this would be the overestimation of rare serious/non-serious adverse events following immunisations (AEFIs) and the underestimation of common mild AEFIs.
• Availability bias is the tendency to assign greater weight to elements that are simpler to recall. The media's portrayal of an unusual serious AEFI report that conveys a strong and compelling anti-vaccine message and is likely to stick in people's minds when making decisions may cause people to overestimate the possibility of an AEFI.
• First-impression bias, also referred to as the anchoring effect, is the tendency to make a decision heavily based on a value that is originally presented. Clinicians may be persuaded to recommend the human papillomavirus (HPV) vaccination to patients based on their age or other physical characteristics, such as their pubertal status. Such initial perceptions might hinder people's subsequent cognitive processing and may encourage greater vaccination hesitancy.
• The propensity to give authoritative persons' opinions greater weight is known as authority bias.
• A tendency towards general distrust in healthcare workers or vaccine products and a focus on negative aspects could be considered negative bias. It could be due to range of factors, including historical events and personal experiences.

2. Cognitive biases during vaccination-related decision-making

• When a person chooses not to take a certain action (omission) rather taking it (commission), even when the consequences of omission are greater than or equal to those of commission, they are exhibiting omission bias, which is the tendency to underestimate the severity of consequences. Parents believe that the adverse events of vaccinations are substantially more severe and long-lasting than the medical sequelae of a sickness.
• The propensity to choose a known risk over an unknown danger, no matter the results, is known as ambiguity aversion. People who choose a known danger from a disease over a vaccination's more unclear risk experience ambiguity aversion, which is one possible cause of vaccine hesitancy.
• Optimism bias is the tendency to have an extremely positive outlook on a particular health risk and believe that it will more likely affect other people than oneself. One example is would be a physician's confidence in her patients' minimal risk of contracting HPV stemming solely from her established personal connect with patients and their families.
• The propensity to prioritise current expenses and advantages above those that will be achieved in the future is known as present bias. People place higher importance on vaccine side effects and expenses since they are visible to the public and available to decision-makers.
• People reject making trade-offs against protected ideals because they are absolute and impervious to interference no matter the consequences. Repercussions are any possible drawbacks from not receiving a vaccination, whereas protected values are any opinions that vaccination contradicts. The subjects do not compromise such values, regardless of the size of the cost, the magnitude of the gain, or the severity of the repercussions. A few examples of protected values are the ability of parents to object to vaccinations and the fact that males are not required to receive the HPV vaccine.
• Information on the Dunning-Kruger effect and status quo biases are provided in Table 2 of the paper.

3. Cognitive biases due to prior beliefs regarding vaccination (which have the strongest influence on vaccine-hesitant individuals)

• Confirmation bias is the tendency to only consider information that confirms our preconceived notions. It thwarts efforts to refute incorrect information that vaccine-skeptical individuals have because they often disregard data that contradict their ideas.
• The propensity to judge an argument's validity based on how credible its conclusion is known as belief bias. It hinders people's cognitive capacities when the understanding of new information conflicts with their preexisting views.
• The propensity to focus more time and effort on information that group members already know and less time and effort on new information is known as shared information bias.
• The false consensus effect refers to the tendency to overestimate the degree to which one's opinions are held by the general public (believing that they are more widely held than they actually are). Poorly informed parents who become involved in online discussions may foster tiny but potent online anti-vaccination communities that lead to attitudes and behaviours that support anti-vaccination ideas. These networks possess a high degree of false consensus regarding vaccine-hesitancy issues.
• A propensity towards the default option when presented with multiple options is known as the default effect. More individuals prefer to select vaccination when it is made the default option.
•  The propensity to follow the majority of other individuals in their decisions is known as the bandwagon effect.
• Details of cognitive dissonance, illusory correlation, and cognitive biases that appeal to nature are presented in Table 3.

"Public health authorities may tailor their strategies, interventions, and other kinds of communication based on the categories presented in this review to downgrade the effects of cognitive biases associated with poor vaccination decisions." For example:

• Communication campaigns may be motivated to address the cognitive biases in group #1, which are common in anti-vaccine content. Initiatives to increase the accessibility information about the benefits of vaccines and disseminate information on more prevalent AEFIs could help lessen the effects of base-rate neglect. More crucially, efforts may be considered to increase trust in vaccines by using biases like the framing effect and authority bias.
• Programme managers may use the specific tools to address the cognitive biases in group #2 as well as mechanisms to inform caregivers about vaccine safety and adverse events (AEs) based on the existing evidence in a manner that enhances confidence in immunisation programmes.
• Careful consideration must be given to reducing the impact of group #3's cognitive biases, which are held by vaccine-hesitant individuals. One method that is generally accepted is to avoid outright rejection or debunking of false information, as that might have the reverse effect, since direct refutation necessitates reiterating falsehoods. Repeating something makes false information easier to remember, which has a beneficial impact on confirmation bias.

All that said, "Raising awareness among the public may lead to people identifying their own biases....There is a need to establish processes, programs, and institutions that encourage critical thinking and consideration of a variety of viewpoints....By doing this, some of these biases may be reduced or even eliminated, and analysis and judgments can make coverage of vaccine acceptance more likely."

In conclusion: "In order to promote innovative approaches to increasing vaccine acceptability and building confidence in the community, an understanding of the impact of relevant cognitive biases is important. This review has attempted to highlight possible cognitive biases that influence vaccination decision-making and communication. These findings would be beneficial for immunization program managers, policymakers, and immunization communication officials to devise multipronged communication strategies to address cognitive biases associated with an intent to boost vaccine acceptance and improve confidence in vaccine uptake decision-making..."