Vaccine Hesitancy: A Structured Review from a Behavioral Perspective (2015-2022)

"Despite the overwhelming benefits of vaccination, vaccine hesitancy (VH) persists as a notable public health dilemma..."

Vaccine hesitancy (VH) has been recognised as a global health challenge, with the resurgence of vaccine-preventable diseases caused by plateauing, or even declining, rates of vaccination coverage in several nations worldwide. Within this study, VH was conceived as a spectrum of attitudes and actions around vaccination, ranging from indecision to choosing to delay or refuse vaccines, in the context of a decision-making process. This paper examines peer-reviewed literature on vaccine hesitancy published from 2015 to 2022, with a specific focus on behavioural perspectives, highlighting the key theories, constructs, variables, contexts, and methods (TCVCM) in VH literature.

Out of 352 VH-related articles, 138 articles were selected for TCVCM analysis. An initial survey of the literature revealed that VH predominantly falls within the scope of preventive health behaviours, with most studies on this topic utilising theories of behaviour and behaviour change as primary theoretical frameworks. Notably, 35% (n = 48) studies did not reference any specific theory in their analyses.

The TCVCM highlighted the prevalence of Social Cognition Theories (SCTs) of attitude and health behaviours in the VH literature, which include the Theory of Reasoned Action (TRA) and the Theory of Planned Behavior (TPB) and Reasoned Action Approach (RAA). Attitude has been identified as a primary psychological antecedent of vaccination intentions, and the role of attitudes in relation to behaviour has been outlined in the TRA and TPB. The RAA combines elements of both theories, while proposing that an individual's skills, as well as environmental factors, moderate the intention-behaviour relationship. In the context of vaccination, vaccine uptake is preceded by vaccination intention, which is a function of attitudes towards vaccines, social norms and perceived behavioural control. Positive intentions to get vaccinated arose when individuals possess the necessary skills to accept vaccines, and there were no environmental factors impeding this acceptance. As with SCTs, the TRA and TBA largely disregard the role of affect in influencing vaccination intentions. However, anticipated regret, viewed as an additional emotive factor in vaccine decision-making, encompasses the negative emotions linked to not performing a particular behaviour.

The Health Belief Model (HBM) proposes that health behaviour is influenced by perceived susceptibility and severity of disease, benefits of a medical intervention, and perceived barriers to engaging in a health behaviour. HBM was applied in efforts to comprehend vaccination behaviours in n = 10 of the studies (7%).

Protection Motivation Theory (PMT) proposes that behaviour is preceded by intention and is influenced by threat and coping appraisals. Threat appraisals involve assessing disease severity and vulnerability, while coping appraisals consider the effectiveness of medical responses, self-efficacy, and barriers to preventive behaviour. The literature reviewed revealed that vaccination intentions were higher when an individual experiences alarming threat appraisals and favourable coping appraisal.

Self Determination Theory (SDT) suggests that autonomous and controlled motivations impact vaccination behaviour, addressing limitations of theories like TRA, TPB, and HBM. Autonomous motivation involves believing vaccination benefits oneself, while controlled motivation stems from external or internal pressures. Both predict vaccination intentions, but only autonomous motivation has been shown to predict both intention and behaviour.

The Terror Management Theory (TMT) posits that individuals are motivated to reduce threats induced from mortality awareness by engaging in conscious and non-conscious psychological defences as coping mechanisms. This motivation can manifest as non-adherence to health behaviours and psychological reactance, which refers to a "set of motivational consequences that can be expected to occur whenever freedoms are threatened or lost" (Brehm & Brehm, 1981).

Several other theories were utilised across VH literature and are discussed in the paper, including Moral Foundations Theory (MFT), Psychological Reactance Theory (PRT), and Framing Theory (FT). Few studies discussed theories associated with group identities and social processes, such as Social Identity Theory, which posits that individuals identify themselves with certain groups (pro- or anti-vaccination) and consider these groups to be superior to those with different views.

The bulk of independent variables used in VH research were individual-level cognitive and affective constructs associated with the various theories (see Table 2 in the paper). These constructs included risk perceptions, attitudes, beliefs and thinking styles connected to vaccination and vaccines, social norms, self-efficacy, intuitive processes such as emotions, moral judgments and motivations, and relationships between these variables and vaccination intentions or behaviours). Furthermore, trust emerged as a major predictor construct of vaccination intention and status.

Variables associated with vaccine-related information were examined across studies analysing information endorsement, media literacy, vaccine knowledge, and belief in misinformation. Information-related behaviours were also investigated, including how information-scanning, -seeking, and -discussing influence vaccination intentions. Access to information from various sources, including public health institutions, healthcare providers, religious leaders, social media, and social support availability, was examined. The sensationalisation of vaccine misinformation via online and social media sources was observed to trigger VH and hamper vaccine uptake.

Policy-level dynamics also played a role in vaccination compliance. Correspondingly, a few studies suggested that social-nudging can be a better alternative to improve vaccine uptake than are mandatory vaccination policies. In addition, public health communication had significant impact on vaccination intentions and behaviours. In this regard, benefit-target framing, loss- and gain-framing, priming notions of collectivism and altruism, and use of different forms of vaccine-related information dissemination mechanisms such as memes, humour, and narratives have been examined in the context of addressing VH.

The most studied dependent variables in VH research could be identified broadly as vaccination intentions. Another frequently utilised construct was vaccination behaviour, described as the act of getting vaccinated, which was also characterised as vaccination acceptance, vaccine-uptake, decisions to vaccinate, and vaccination compliance. Vaccination attitudes and beliefs also served as dependent variables.

The TCVCM analysis identified the countries from which VH research originated (see Table 4), type of vaccines, and samples examined by researchers (see Table 5). Finally, the TCVCM analysis identified a range of study designs and methodologies used in the VH literature (see Table 6).

Based on this analysis, a schema of overall factors was developed (see Figure 2) that codifies research on VH and illustrates the many determinants VH studies have identified as affecting vaccine decision-making. This systematisation reaffirms the complexity of VH. Rather than being able to establish simple relationships between VH and any single psychological, social, or cultural characteristic, the sample of VH literature reveals an array of individual-related factors, social connections, demographics, organisational conditions, and policy influences that may be at play in vaccine decision-making. This complexity can also complicate vaccine advocacy efforts.

The TCVCM analysis identified several directions for future research, such as the need to conduct more contextual studies in low- and middle-income nations to bring out the cross-cultural nuances of VH. Further research is also needed to understand public discourses regarding vaccines to reveal collective sentiments in various contexts and across different social media platforms.

While acknowledging the broad scope of theories that have been used in the VH literature, the researchers suggest that other behaviour adoption theories may serve future VH investigations to better understand vaccine decision-making, as well as aid in the design and implementation of new vaccine advocacy strategies. Such theories encompass the Extended Parallel Process Model  and the Health Action Process Approach, along with integrative frameworks such as the Capability-Opportunity-Motivation-Behavior (COM-B) model, the Behavior Change Wheel, and the Theoretical Domains Framework.