Introduction

Vaccination and antibiotics are the main approaches used to control infectious diseases in human populations and communities. With sanitation and clean water, vaccines are estimated to have saved more lives over the past one hundred years than any other health intervention. Vaccination has been responsible for the eradication of smallpox in 1980 and the containment or control of many infectious diseases once common such as rubella, diphtheria, or polio (Khan & Smith, 2010; Rappuoli, 2014).

Yet despite the strong scientific and medical consensus regarding the importance of vaccines as a means to prevent diseases in individuals and control outbreaks in populations, a nonnegligible proportion of the population, including healthcare providers, is skeptical about the usefulness and safety of vaccination. Recent outbreaks of vaccine-preventable diseases in high-, middle-, and low-income countries have been linked to vaccine refusals (Omer, Salmon, Orenstein, deHart, & Halsey, 2009; Phadke, Bednarczyk, Salmon, & Omer, 2016). The concept of “vaccine hesitancy” is now frequently used in discussions around vaccine acceptance to reflect ambivalence toward vaccination.

Of course, vaccine hesitancy is not a novel phenomenon. There has been a resistance in the adoption of vaccination since the 18th century, when the first vaccination program against smallpox was introduced in Europe (Blume, 2006; Colgrove, 2016; Durbach, 2005). Many of the arguments used by the antivaccination activists in the 1800s are still echoed today (e.g., vaccines are ineffective, are used to make profit, contain dangerous substances, natural is better) (Wolfe & Sharp, 2002). However, a growth in vaccine hesitancy is frequently invoked and is associated with different contemporary factors (Cooper, Larson, & Katz, 2008). Declining trust in institutions and greater reliance on experiential knowledge and social networks (Sobo, 2016; Ward, 2017) or the negative influence of controversies around vaccines in the media, especially in the internet and social media (Betsch & Sachse, 2012; Kata, 2012) are frequently used to explain the increase in vaccine hesitancy (i.e., anyone and everyone can now have a large audience for fringe views).

The purpose of the current article is to define vaccine hesitancy and its determinants. Promising strategies to address vaccine hesitancy will also be presented as well as the causes and consequences of vaccine hesitancy among healthcare providers.

Vaccine Hesitancy: Definition and Measures

The WHO Strategic Advisory Group of Experts (SAGE) has endorsed the Working Group on Vaccine Hesitancy definition of vaccine hesitancy as “delay in acceptance or refusal of vaccines despite availability of vaccine services” (MacDonald, 2015). According to this group, the scope of vaccine hesitancy includes instances where “vaccine acceptance in a specific setting is lower than would be expected, given the availability of vaccination services” (MacDonald, 2015). The risk of vaccine hesitancy is higher in situations of passive acceptance of vaccines (i.e., compliance by a public that yields to recommendations and social pressure) (Nichter, 1995). In contrast, when “vaccine demand” exists (i.e. in situations where individuals and communities seek, support, and/or advocate for vaccines and immunization services) the risk that vaccine hesitancy develops is much lower (Hickler et al., 2017). The concept of vaccine hesitancy implies that, beyond the traditional binary of pro- or antivaccine attitudes, a spectrum of beliefs and associated behaviors occupies the space between the two poles (Figure 1). A vaccine-hesitant person can occupy different (or many) places along this continuum of perspectives and can delay vaccination or refuse one, some, or all vaccines (Dubé et al., 2013; Hilton, Petticrew, & Hunt, 2006; Kennedy, Lavail, Nowak, Basket, & Landry, 2011). Even people who accept all recommended vaccination or have their child fully vaccinated can still have serious doubts and worries and be considered as vaccine-hesitant (Hilton et al., 2006; Kennedy et al., 2011; My, Danchin, Willaby, Pemberton, & Leask, 2017). Vaccine hesitancy is multidimensional and context-specific, varying across time, place and vaccines (Larson, Jarrett, Eckersberger, Smith, & Paterson, 2014; MacDonald, 2015).

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Figure 1. The vaccine attitude continuum.

Because it is a complex issue, application of the concept of vaccine hesitancy can be challenging (Peretti-Watel, Larson, Ward, Schulz, & Verger, 2015). Promising tools to assess vaccine hesitancy have been developed and validated in the United States (Gilkey et al., 2016; Martin & Petrie, 2017; Opel et al., 2011). The most widely known is the Parent Attitudes about Childhood Vaccines survey (PACV). The PACV was developed by Opel and collaborators and has been shown to be a reliable tool to identify vaccine-hesitant parents and predict underimmunization in their infant. The tool was successfully adapted to other cultural contexts (Mohd Azizi, Kew, & Moy, 2017). However, the evidence is mixed regarding its use in other population groups, such as parents of teenagers (Roberts et al., 2015; Strelitz et al., 2015). There is still a need for validated tools that can identify patterns of vaccine hesitancy in individuals, subgroups, and populations over time, differentiating outright refusers from the hesitant (Larson et al., 2015; Leask, Willaby, & Kaufman, 2014). Validated tools to assess hesitancy among adults and seniors are lacking. Because research has mainly focused on the metrics of vaccine uptake (coverage rates, delays, refusals), the degrees to which vaccine hesitancy influences vaccination behaviors remains an important, but complex, domain for investigation (Eskola, Duclos, Schuster, & MacDonald, 2015). For instance, all national immunization program managers were asked to report on the impact of vaccine hesitancy in their country in the 2014 World Health Organization and United Nations Children’s Fund Joint Reporting Form (JRF) on immunization. Of the 194 countries who completed the JRF, 74 percent reported that vaccine hesitancy was an issue in their country. However, only 29 percent of the member states reported having done studies to better understand the cause and impact of vaccine hesitancy in their country (Marti, de Cola, MacDonald, Dumolard, & Duclos, 2017).

Furthermore, because the factors influencing vaccine hesitancy not only vary within and between populations and subgroups but also according to context, time, and vaccine, diverse types of data and measurement approaches are needed to capture, quantify, and describe hesitancy (Larson & Schulz, 2015). For instance, the use of social media could complement traditional research methods and allow for real-time access to the attitudes, beliefs, and opinions of vaccine-refusers, a group who often fall outside traditional sampling approaches (Dredze, Broniatowski, Smith, & Hilyard, 2016). Longitudinal monitoring of vaccine hesitancy using comparable methods such as tracking surveys will also be crucial to monitor temporal shifts over time and geographically (Campbell et al., 2017; Frew et al., 2016).

Determinants of Vaccine Hesitancy

A myriad of factors have been associated with vaccine hesitancy (Larson et al., 2014). At the individual level, recent reviews have identified determinants such as low perception of the efficacy and usefulness of vaccines; concerns about vaccine safety and fear of side effects; distrust in healthcare providers and the health system; perceptions around health and prevention and a preference for “natural” health; fear of pain at immunization and fear of needles; negative past experiences with vaccination services; and lack of awareness or knowledge about vaccination as well as different sociodemographic factors (e.g. age, revenue, level of education) (Cobos Munoz, Monzon Llamas, & Bosch-Capblanch, 2015; Dubé et al., 2013; Forster et al., 2016; Larson et al., 2014; Yaqub, Castle-Clarke, Sevdalis, & Chataway, 2014). Given the broad spectrum of these views, it is difficult to assess the relative strength of influence of each of these factors. For instance, education and socioeconomic status have been associated with vaccine hesitancy, but not as usually seen for other health issues where higher level of education and socioeconomic status are associated with better health conditions or better adherence to public health recommendations. Instead, increased vaccine hesitancy has been associated with both high and low education and high and low socioeconomic status, highlighting the complex array of interrelated factors at play (Amit Aharon, Nehama, Rishpon, & Baron-Epel, 2017; Berezin & Eads, 2016; McNutt et al., 2016).

At the individual level, different cognitive processes can also trigger vaccine hesitancy (Brewer et al., 2007; Casiday, 2007; Hobson-West, 2003; Lagoe & Farrar, 2014). Decision-making about vaccines is influenced by cognitive biases, or heuristics, which are mental shortcuts that allow people to solve problems and make judgments quickly and efficiently when faced by uncertainties and risk (for a review see MacDonald, Smith, & Appleton, 2012). For instance, risks that are common or familiar are more acceptable to people than risks that are uncommon or unknown (Blaisdell, Gutheil, Hootsmans, & Han, 2016). In addition, choices are much more linked with how people feel about the facts than to the facts themselves—even if they do correctly understand these facts (Peters & Bjalkebring, 2015; Slovic, 1987). Risks to children feel more serious than risks to adults because children are vulnerable; risks from the vaccine feel more real because they seem more proximate than the actual disease being prevented (Ropeik, 2013). Furthermore, individuals are “cognitive misers,” collecting only as much information as they think is needed to reach a decision (Nisbet, 2014). Research has also shown that people’s beliefs about the harms and benefits pertaining to vaccination—and their beliefs about what other people think about the evidence—vary as a function of their political ideology and cultural worldviews (Kahan, 2013; Kahan, Braman, Cohen, Gastil, & Slovic, 2010; Larson et al., 2016; Rabinowitz, Latella, Stern, & Jost, 2016). People are also more drawn toward, and accepting of, information and its sources that share their worldview (Kahan, Braman, et al., 2010; Kahan, Jenkins-Smith, & Braman, 2010). Trust in experiential knowledge, a mother’s “natural” instinct, and other advice given within the parents’ social network against vaccinating can be more influential in a parent’s vaccination decision than scientific evidence or experts with professional qualifications (Bish, Yardley, Nicoll, & Michie, 2011; Brunson, 2013; Gesser-Edelsburg, Walter, Shir-Raz, Sassoni Bar-Lev, & Rosenblat, 2017; Hershey, Asch, Thumasathit, Meszaros, & Waters, 1994; Johnson & Capdevila, 2014; Kaufman, 2010; Streefland, Chowdhury, & Ramos-Jimenez, 1999; Sturm, Mays, & Zimet, 2005). In her study of highly educated affluent mothers who rejected recommended vaccines, Reich has shown how mothers trusted their judgement as mothers more than they trusted experts on the risks of vaccines and diseases, believed that their own “family’s healthful living” was better than vaccines to keep their children healthy, and felt confident they could avoid the risks of vaccine-preventable diseases by controlling their children’s social networks and exposures to “outsiders” who might infect them (Reich, 2014). In summary, individuals perceive risk of vaccines in different and unique ways that reflect their cultural, emotional, social, and political worlds (Driedger, Maier, Furgal, & Jardine, 2015; Dubé et al., 2013; Reyna, 2012). For instance, vaccine hesitancy among Aboriginal populations in Canada that were prioritized to receive the A(H1N1) vaccine due to their higher rate of infection had much more to do with collective colonial experiences, histories of racism, and social exclusion than about their understanding of the characteristics of the vaccine or the diseases (Driedger, Cooper, Jardine, Furgal, & Bartlett, 2013; Driedger et al., 2015).

Social sciences research has shown that vaccination decisions are part of a “wider social world” and that vaccine hesitancy needs to be understood in the broader social, cultural, historical and political landscapes that “gives shape to ideas and ideals” about health, prevention, and what a good parent does about vaccination (Kaufman, 2010; Poltorak, Leach, Fairhead, & Cassell, 2005). A confluence of social factors, such as social identities and social norms, contribute to vaccine hesitancy (Forster et al., 2016; Gesser-Edelsburg et al., 2017). In communities outside of the “mainstream” (i.e., communities adopting alternative lifestyles), vaccine hesitancy and refusals can serve to reinforce social identities (Attwell, Leask, Meyer, Rokkas, & Ward, 2017; Sobo, Huhn, Sannwald, & Thurman, 2016), while in low-income countries vaccine refusals can be seen as a way for economically and politically deprived communities to express dissatisfaction with wider socioeconomic conditions via the program to the state (Taylor, 2015).

The decreasing levels of trust in institutions and medical science has also been associated with increased vaccine hesitancy in both empirical and theoretical literatures (Johnson & Capdevila, 2014; Ward, 2017; Yaqub et al., 2014). Findings of quantitative and qualitative studies have shown that parental distrust of the government and of healthcare providers was a significant factor related to a number of vaccine-related beliefs and behaviors (Attwell et al., 2017; Lee, Whetten, Omer, Pan, & Salmon, 2016).

The media also contribute to vaccine hesitancy. The negative influence of vaccine controversies communicated by the traditional media (e.g., newspapers, magazines, television) on vaccine uptake has been well documented (King & Leask, 2017; Odone & Signorelli, 2017). Routine media coverage of celebrities declining vaccination or questioning the safety of vaccines has also been shown to have a detrimental effect on vaccine acceptance in the public (Hoffman & Tan, 2013; Mnookin, 2011; Offit, 2013). Two-sided news messages with claims both for and against vaccines can lead readers to erroneously infer the state of expert knowledge regarding vaccine safety and negatively impact vaccine intentions (Dixon & Clarke, 2013). Results of an experimental study on news stories designed to evoke either fear or hope about human papillomavirus (HPV) have shown that news stories may influence behavior not necessarily from what they say but from the prior knowledge they might prime about effective action (Nabi & Prestin, 2016).

Information about vaccination that circulates in Internet and social media is also frequently associated with the growth of vaccine hesitancy (Bragazzi et al., 2017; Davies, Chapman, & Leask, 2002; Larson et al., 2013; Scullard, Peacock, & Davies, 2010; Witteman & Zikmund-Fisher, 2012; Wolfe, Sharp, & Lipsky, 2002; Zimmerman et al., 2005). Research has shown that the quality of vaccination-related information on websites or social media platforms is highly variable, with a substantial volume of negative and inaccurate information (Witteman & Zikmund-Fisher, 2012). An analysis of social media sites dedicated to discussions of parenting has found that in most vaccination stories, it is taken for granted that vaccines and not vaccine-preventable diseases pose a threat to children; because vaccines are seen as a threat, parents focus on sharing successful strategies for avoiding them (Tangherlini et al., 2016). Indeed, many studies have shown that individuals who delayed or refused vaccines are significantly more likely to have looked for vaccine information on the Internet (Betsch & Sachse, 2012; Brunson, 2013; Fabry, Gagneur, & Pasquier, 2011; Wheeler & Buttenheim, 2013). Viewing antivaccination websites and reading personal stories about negative consequences of vaccination has also been associated in experimental studies with an increase in users’ vaccine hesitancy (Betsch, Renkewitz, Betsch, & Ulshofer, 2010; Betsch, Renkewitz, & Haase, 2013; Jolley & Douglas, 2014; Nan & Madden, 2012). A study that measured information exposure derived from Twitter to explain differences in coverage in the United States has shown that vaccine coverage was lower in states where safety concerns, misinformation, and conspiracies made up higher proportions of exposures, suggesting that negative representations of vaccines in the media may reflect or influence vaccine acceptance (Dunn et al., 2017).

In summary, vaccine hesitancy is caused by a complex mix of interrelated factors ranging from the social and cultural context; the influences of social networks; the individual’s own perceptions, values and experiences to the vaccine; and vaccination services themselves (e.g., mode of administration, vaccination schedule, design of the vaccination program) (MacDonald, 2015).

The WHO SAGE working group on vaccine hesitancy has summarized the complex array of factors influencing vaccine hesitancy into the “3Cs model” for confidence, complacency, and convenience. Vaccine confidence is defined as trust in a) the effectiveness and safety of vaccines; b) the system that delivers them, including the reliability and competence of the health services and health professionals and c) the motivations of the policymakers who decide which vaccines are needed when and where. Vaccine complacency exists where perceived risks of vaccine-preventable diseases are low and vaccination is not deemed a necessary preventive action. Complacency about a particular vaccine or about vaccination in general is influenced by many factors including other life or health responsibilities or both that may be seen to be more important at that point in time. Vaccine convenience is measured by the extent to which physical availability, affordability and willingness-to-pay, geographical accessibility, ability to understand (language and health literacy), and appeal of immunization services affect uptake. The quality of the service (real or perceived) and the degree to which vaccination services are delivered at a time and place and in a cultural context that is convenient and comfortable also affects the decision to be vaccinated (MacDonald, 2015).

Strategies to Address Vaccine Hesitancy

In the midst of the 2015 measles outbreak, there were call for a “gloves off” approach to address the issue of vaccine hesitancy and refusal (Rainford & Greenberg, 2015). Some experts were calling for stronger policies to enforce mandatory immunization, some physicians were dismissing families refusing vaccines, and some parents were publicly saying that their immunocomprised children were endangered by the “irresponsible” parents who refused to vaccinate their healthy kids. While it can make vaccine advocates feel good, blaming and shaming people who refuse vaccination is unlikely to change their minds (Witteman, 2015). In addition, while mandatory vaccination policies can effectively increase vaccine uptake, they do not adequately address the underlying causes of vaccine hesitancy and refusal (Adams et al., 2016; Lee & Robinson, 2016; Wigham et al., 2014).

What can be done to effectively address vaccine hesitancy? Recent reviews have specifically examined the literature around strategies to address vaccine hesitancy in the population, but did not identify any convincing evidence on effective interventions (Jarrett et al., 2015; Sadaf, Richards, Glanz, Salmon, & Omer, 2013; Williams, 2014). A summary of the findings from 15 published literature reviews or meta-analyses that have examined the effectiveness of different interventions to reduce vaccine hesitancy showed that, although some studies reported a statistically significant improvement on vaccine uptake, the data were very inconsistent and, most of the time, the evidence was of low or moderate quality. Very few interventions were directly targeted to vaccine-hesitant individuals (Dubé, Gagnon, MacDonald, & Sage Working Group on Vaccine Hesitancy, 2015).

Vaccine hesitancy is a wicked public health issue. Wicked problems are by their very nature persistent and hard to resolve because they do not lend themselves to a scientific consensus about the source of the problem or the best means for resolving it (Rittel & Webber, 1973). As of today, there is no agreement on how best to use communication to respond to vaccine hesitancy (Greenberg, Dubé, & Driedger, 2017). The literature, however, does suggest some key principles for optimizing the development of strategies to tackle vaccine hesitancy. Public health and health professional communications need to move beyond the “knowledge deficit model” to adopt more effective communication strategies (Goldenberg, 2016; Rossen, Hurlstone, & Lawrence, 2016). As described previously, people are complicated, with different underlying values and priorities that can compete with public health recommendations (Driedger et al., 2013; Masse & Desy, 2014). Information is important in the decision-making process around vaccination (Lieu, Zikmund-Fisher, Chou, Ray, & Wittenberg, 2017; Mus, Kreijkamp-Kaspers, McGuire, Deckx, & van Driel, 2017). However, simply communicating information about vaccine safety and efficacy to those who are vaccine hesitant is clearly insufficient to stem the growth of hesitancy-related beliefs and fears (Dubé, Gagnon et al., 2015). More information on vaccines does not result automatically in more trust in vaccines (Cataldi, Dempsey, & O’Leary, 2016; Scherer, Shaffer, Patel, & Zikmund-Fisher, 2016). Worst, pro-vaccine messages can have unintended and undesirable consequences such as increasing resistance to vaccination (Nyhan & Reifler, 2015; Nyhan, Reifler, Richey, & Freed, 2014). These backfire effects can occur when interventions are designed without taking into consideration key principle from psychology regarding how people think and act (Buttenheim & Asch, 2016; Rossen et al., 2016). Effective risk communication strategies need to capitalize on heuristics rather than try to fight against it (Blaisdell et al., 2016; Scott, Soon, Elshaug, & Lindner, 2017). Successful communication is “a two-way process, an equal measure of listening and telling. Understanding the perspectives of the people for whom immunization services are intended, and their engagement with the issue, is as important as the information that experts want to communicate” (Goldstein, MacDonald, & Guirguis, 2015). From a programmatic perspective, managing risk communication is especially important when situations occur in which adverse events are rightly or wrongly associated with vaccination. The WHO Regional Office for Europe has recently published a background document presenting scientific evidence about social and psychological factors that drive a vaccine safety crisis and presenting effective strategies on how to communicate risk and to shape messages to the audiences to mitigate crises (World Health Organization Regional Office for Europe, 2017).

Effective public health interventions to address vaccine hesitancy should also be developed using a planning framework, such as the WHO Guide to Tailoring Immunization Programmes that provides tools to identify vaccine hesitant population subgroups, to diagnose the barriers and enablers for vaccination in these subgroups, and to design evidence-informed responses to vaccine hesitancy appropriate to the setting, context, and hesitant subgroup, including tailored communications (Butler & MacDonald, 2015; World Health Organization Regional Office for Europe, 2013).

Finally, if social contagion has a negative impact on vaccine acceptance, this collaborative community approach can also be used to positively shift the negative vaccination discourses and address vaccine hesitancy (Buttenheim & Asch, 2016). Different initiatives that have mobilized parents who value vaccination and provided them with tools to engage in positive dialogue about immunizations in their communities have shown promising results (Attwell & Freeman, 2015; BC Centre for Disease Control & Public Health Association of British Columbia, 2017; Schoeppe et al., 2017).

Vaccine Hesitancy and the Healthcare Providers

Healthcare providers have a key role to play in risk communication about vaccination and are one of the most trusted source of information (Favin, Steinglass, Fields, Banerjee, & Sawhney, 2012; Hwang et al., 2017; Wheeler & Buttenheim, 2013; Yaqub et al., 2014). One of the main drivers of vaccine acceptance is receiving a recommendation for vaccination by a health care professional (Gust, Darling, Kennedy, & Schwartz, 2008; Schmitt et al., 2007; Stefanoff et al., 2010). For instance, a study conducted by Gust et al in the United States concluded that information or reassurance from a healthcare provider was the main factor in changing the decision of parents who had planned to delay or refuse a vaccine for their child (Gust et al., 2008).

Healthcare providers’ knowledge and attitudes about vaccines are an important determinant of their own vaccine uptake, their intention to recommend the vaccine to their patients, and the vaccine uptake of their patients (Herzog et al., 2013; Killian et al., 2016; Zhang, While, & Norman, 2010). Belief that the vaccine is safe and effective, perceived risk of disease in the absence of vaccination, past vaccination behaviors, social norms, and ease of access to the vaccines were key determinants of vaccine uptake among healthcare providers themselves (Prematunge et al., 2012; Vasilevska, Ku, & Fisman, 2014; Yaqub et al., 2014).

Risk communication about vaccines, however, can be emotional for both parents and healthcare providers as ideological positions that may not be in sync (Kempe et al., 2015). Providers’ sense of professional identity as health advocates and experts can be challenged in their encounters with vaccine-hesitant and vaccine-refusing patients (Berry et al., 2017). A recent review of the literature around providers’ communication practices with vaccine-hesitant parents has concluded that, although there is not enough information to definitively state the type of provider-patient communication most effective in enhancing vaccine acceptance, a participatory type of interaction was the most promising (Connors, Slotwinski, & Hodges, 2017). Results of observational studies have however indicated that presumptive rather than participatory initiation of vaccine recommendations appears to increase patients’ acceptance of vaccination (Hofstetter et al., 2017; Opel et al., 2013). By presumptively introducing the discussion around vaccination, healthcare providers reinforce the importance of vaccination by assuming that this is the “normal thing to do.” However, if parents oppose or raise concerns, then a more participatory approach of listening and addressing doubts is warranted (Leask & Kinnersley, 2015; Witteman, 2015).

When healthcare providers communicate effectively with parents about vaccine benefits and risks, the value and need for vaccinations, and vaccine safety, parents are more confident in their decisions (Cawkwell & Oshinsky, 2016). However, to do this well, healthcare providers need to be confident themselves about the safety, effectiveness, and importance of vaccination. Research has shown that a significant proportion of healthcare providers, including those who administer vaccines, are vaccine hesitant in their personal and professional lives (Dubé et al., 2016; Karafillakis et al., 2016; Killian et al., 2016; Prematunge et al., 2012; Verger et al., 2015). For instance, a study of vaccination practices and attitudes among general practitioners in France has shown that up to 43 percent of the surveyed practitioners were not recommending vaccination to their target patients and that many were disagreeing with statements about the safety and usefulness of vaccines (Verger et al., 2015). In another study, up to 60 percent of the French practitioners were also doubtful regarding the safety of the HPV vaccine and almost a quarter of those with daughters did not intend or did not have their daughters vaccinated (Collange et al., 2016). A review of studies published before October 2015 on vaccine hesitancy among healthcare providers has shown that providers’ knowledge about particular vaccines’ efficacy and safety was key in building their confidence and willingness to recommend the vaccines to others. Few effective strategies to address vaccine hesitancy among healthcare providers were identified in this review (Paterson et al., 2016).

Conclusion

From the Emmy-winning 1982 documentary entitled DTP: Vaccination Roulette—alleging that the vaccine’s pertussis component was causing severe brain damage, seizures, and mental retardation—to the purported link between measles, mumps, and rubella (MMR) vaccination and autism or to the boycott of the polio vaccine in northern Nigeria in 2003 due to fears that the vaccine was a Western plot to spread infertility and HIV among Muslims (Dubé, Vivion, & MacDonald, 2015; Kapp, 2003; Taylor, 2015), several vaccine controversies have traveled worldwide over the past decades. These controversies, along with an erosion of trust in health authorities, experts, and science, have made public health authorities aware that widespread acceptance of vaccines cannot be taken for granted. The growth of vaccine hesitancy has been the focus of much attention in the past decade and is now recognized as a serious global threat to the success of vaccination programs (Hickler, Guirguis, & Obregon, 2015). The wealth of knowledge generated in this growing field of research about how “humans actually behave, not around how they ought to behave” from a public health standpoint need to be used to develop, implement, and evaluate tools and interventions to better understand and address this complex problem (Buttenheim & Asch, 2016).