Beyond Confidence: Development of a Measure Assessing the 5C Psychological Antecedents of Vaccination

"There is considerable debate among practitioners and academics from all parts of the world about how to measure hesitancy right, whether hesitancy is the best term, how general such a measure can or should be, and how context-specific vaccine hesitancy is."

There is a growing number of measures to define and measure vaccine hesitancy or confidence, such as the Parent Attitudes about Childhood Vaccines survey (PACV), the Vaccine Confidence Scale (VCS), a set of 4 items forming a Global Vaccine Confidence Index (GVCI), the Vaccine Hesitancy Scale (VHS), the Vaccine Acceptance Scale (VAS), and the Vaccine Confidence Index (VCI). Most existing measures assessing vaccine hesitancy focus primarily on confidence in vaccines and the system that delivers them. However, empirical and theoretical work has found that complacency (not perceiving diseases as high risk), constraints (structural and psychological barriers), calculation (engagement in extensive information searching), and aspects pertaining to collective responsibility (willingness to protect others) also play a role in explaining vaccination behaviour. The objective of this study was therefore to develop a validated measure of these "5C" psychological antecedents of vaccination. The researchers conducted 3 studies with nearly 2,800 participants testing its convergent, discriminant, and concurrent validity, resulting in a long (15-item) and short (5-item) version of the scale.

Before describing the scale's development process in detail, the researchers provide an overview of several models explaining vaccination behaviour and existing measures to assess its determinants. Hesitancy describes a continuum between complete acceptance and complete refusal. The factors complacency, convenience, and confidence - referred to as the 3C model - have been identified based on experience in various countries and extensive literature review. Table 1 in the article provides their exact definitions. The definitions show that these factors comprise several concepts from psychological theories for predicting prevention behaviour. For example, confidence includes behavioural beliefs about vaccination (knowledge), which relate to attitudes towards vaccination. In previous work, the researchers therefore suggested constellations of psychological predictors that match the hesitancy factors' definitions, referring to established theoretical frameworks, such as the Health Belief Model and the Theory of Planned Behavior. They then extended the 3C model to a 4C model by integrating calculation (the individual's engagement in extensive information searching) as an additional psychological antecedent. This factor captures the individual motivation of thinking about and questioning vaccination and is often positively correlated with vaccine hesitancy. The 5A taxonomy for explaining vaccine uptake provides a somewhat different terminology. It is based on a narrative review and identifies 5 categories: acceptance, access, affordability, awareness, and activation.

The next section of the article defines all 5 psychological antecedents of vaccination represented in the 5C scale - confidence, complacency, constraints, calculation, and collective responsibility - and derives relations to validation constructs (for a summary, see Table 2). Each antecedent represents individual preferences or psychological, mental representations of the environment the respondent lives in.

Three cross-sectional studies were conducted. Study 1 used factor analysis to develop an initial scale and assesses the sub-scales' convergent, discriminant, and concurrent validity (N = 1,445, two German convenience-samples). The scale in its version after Study 1 did not include the awareness of the social benefit, yet research has shown that people do care about others when making vaccination decisions, and communicating the social benefit of vaccinations leads to a higher willingness to vaccinate. However, knowing about herd immunity may also instigate free-riding. In order to capture the tendency to either vaccinate with pro-social intentions or to selfishly opt out, Study 2 added items to assess collective responsibility. In Study 2, a sample representative regarding age and gender for the German population (N = 1,003) completed the measure for vaccination in general and for specific vaccinations to assess the potential need for a vaccine-specific wording of items. Study 3 compared the novel scale's performance with 6 existing measures of vaccine hesitancy (N = 350, United States (US) convenience-sample).

As an outcome, a long (15-item) and short (5-item) 5C scale were developed as reliable and valid indicators of confidence, complacency, constraints, calculation, and collective responsibility. The 5C sub-scales correlated with relevant psychological concepts, such as attitude (confidence), perceived personal health status and invulnerability (complacency), self-control (constraints), preference for deliberation (calculation), and communal orientation (collective responsibility), among others. In a comparison of 7 measures, the 5C scale was constantly among the scales that explained the highest amounts of variance in analyses predicting single vaccinations (between 20% and 40%; Study 3). In short, the 5C sub-scales are valid predictors of vaccination behaviour for several vaccinations, and the amount of explained variance was relatively high.

In summary, the studies showed that the pattern of significant predictors varies depending on the vaccination at hand and the target or risk group, as well as country. This is a result that holds for all existing scales. For example, in Study 2, flu vaccination was related to 4 factors in elderly Germans, while only one factor predicted flu vaccination in US parents. This seems to mirror the notion that vaccine hesitancy is complex and context specific. Moreover, the analyses showed that the general version of the 5C scale (asking for vaccination in general) predicted acceptance as similarly well as a vaccine-specific version (e.g., asking specifically for influenza vaccination).

By relating the 5C sub-scales to psychological constructs, the researchers learned more about the psychological underpinnings of vaccine hesitancy and acceptance, as described in the results of Studies 1 and 2 (summary in Table 2). If one were to construct "psychological profiles" of the extreme ends of the scales, a person that lacks confidence is more likely to have a negative attitude and misbeliefs, to mistrust the health system and medical treatments in general, and to believe in conspiracies. A person who is held back due to constraints also has a more general lack of self-control and self-efficacy. Highly constrained people perceive a lack of time, so for these people vaccination should be made easy. The typical complacent person does not feel vulnerable, feels healthy, and does not care about the future, which might lead to high-risk behaviours. Disease risks are perceived as low. People who calculate are risk averse, prefer to deliberate, and are especially concerned about the risks associated with vaccination. Even though deliberation and risk assessments are important, the respective skills (numeracy) are not especially high in these people, which potentially leads to skewed risk perceptions (high vaccination risks, low disease risks). People who score high on collective responsibility generally care more for other people and are more empathic.

According to the researchers, a broader analysis that explores the basic causes of the identified antecedents that combines qualitative and quantitative analyses is necessary to develop behaviour change interventions. For example, a lack of confidence may be related to misinformation; however, it may also be related to a political system fostering inequality. Future research could identify interventions that match the relevant C(s) - e.g., which interventions are best suited to overcome constraints, to increase confidence, to reduce complacency (without increasing psychological reactance), etc. In addition, addressing more than one underlying cause in one intervention is likely to increase the success of the intervention.