Vaccine Hesitancy, Acceptance, and Anti-Vaccination: Trends and Future Prospects for Public Health

"The COVID-19 pandemic has heightened global awareness on the importance of understanding complex political, social, and behavioral factors influencing public acceptance of effective, scientifically rigorous, and ethically sound recommendations to reduce transmission, including future vaccine acceptance."

The past 10 years have seen an increasing number of studies on the topic of vaccine hesitancy, which has been defined as the reluctance or refusal to vaccinate despite availability of vaccines. The phenomenon is complex and varies for different vaccines and across time and contexts. This review provides an overview of literature on the topic, starting with a discussion of terminology and concepts before looking at potential causes, consequences, and impacts of resistance to vaccination.

To begin, the authors make three clarifications:

• Despite the importance of access, affordability, and awareness - three of the "As" within the frame of the oft-cited 5 As model - this article is focused mainly on acceptance and activation of vaccination, which refer to how vaccine recipients and vaccine providers understand and engage in immunisation.
• "Anti-vaccine" is not the same as "vaccine hesitant". Instead, vaccine hesitancy captures behaviour that lies along on a spectrum ranging from active demand for vaccines to complete refusal of all vaccines. Vaccine-hesitant individuals are a heterogeneous group along this continuum.
• Even the concept of vaccine hesitancy has been the subject of different definitions. Yet, per the authors, it should be used to refer to situations where people have doubts and concerns about vaccines, without referring to actual vaccine receipt (e.g., vaccination may be mandatory to attend school or to travel, but vaccine hesitancy still exists).

Next, the authors disentangle what is old and what is new in vaccine criticism in order to understand its appeal in such different historical contexts. From 1796 through to the present day, proponents of a wide variety of medical philosophies (in high-, middle-, and low-income settings) have rejected the principle of vaccination. Debates over the safety of vaccines have multiplied since 2009, revealing the age-old but important existence of less radical forms of vaccine criticism. In the case of concerns over the vaccine against human papillomavirus (HPV), the media gave voice to the actors who distanced themselves from anti-vaccination activists and presented arguments restricted to that particular vaccine. This example also arises as the authors examine the wide variety of forms of the politicisation of vaccines, which depends on local contexts and vaccines. The introduction of the vaccine against HPV illustrates this point. In the United States, some conservative and religious groups criticised the association between the vaccine and sexuality, whereas in France, the early vocal critics of the vaccine were found among very progressive and environment-friendly activists who were concerned about the fact that the vaccine contained aluminum. The case of HPV vaccination also underlines the importance of vaccine mandates in the genesis of vaccine-critical activism.

Turning to vaccine resistance in low- and middle-income countries (LMICs), the authors note that tendency to associate vaccine refusal with traditions, alternative conceptions of health, and religion is even stronger in discourses on vaccine resistance than in some other parts of the world. Furthermore, issues that emerge elsewhere tend to be exacerbated in the midst of corruption, political instability, weak public institutions, and ethnic tensions. In some contexts (e.g., in the case of the oral polio vaccine, or OPV), resistance to vaccination can be a way to garner other interventions to meet community needs such as safe water and access to health services.

As reported here, work is underway at the global level to develop a set of tools to measure and address the reasons for undervaccination and to track consistent and comparable data over time. Such longitudinal monitoring could not only facilitate tracking of temporal and geographical shifts in hesitancy and approval but also enable evaluation of the possible negative consequences of vaccine-critical discourses. For instance, data could quantify the impacts of vaccine controversies, shared via traditional media (e.g., newspapers, magazines, television), on vaccine uptake. The media's quest to be balanced (presenting both sides of a news story, even if one side has no merit) can negatively impact vaccine intentions by giving the impression there is no scientific consensus regarding vaccine safety and efficacy.

The internet and social media also play a key role in vaccine hesitancy. For example, studies testing the impact of fictitious websites and/or vaccines have demonstrated that viewing vaccine-critical internet-based content and reading personal stories about negative consequences from vaccines increase users' risk perceptions about vaccination and decrease intention to vaccinate. Compounding exposures to negative messages are features of internet search engines that filter information to reflect an individual's previous search patterns. As such, if a user is searching and follows links related to hesitancy or refusal, he or she is more likely to be exposed to such content in future searches. Some social media platforms have taken steps to limit the circulation of vaccine misinformation online, but many groups opposed to vaccine(s) have managed to move beyond these restrictions.

For most people, physicians and nurses are trusted sources for vaccine information. However, some vaccine-hesitant individuals have found it difficult to have an open discussion about vaccination with their physician, particularly in light of the fact that a significant proportion of healthcare providers are themselves vaccine hesitant. Given evidence of providers' critical role in maintaining vaccine acceptance, the authors suggest that understanding and addressing the specific concerns of mainstream and complementary and alternative medicine (CAM) providers along the vaccine hesitancy spectrum is one of the steps to take to ensure that confidence in vaccination is strengthened rather than undermined in the clinical encounter.

The authors explore several approaches to dealing with vaccine critics. Using psychological research on persuasion as well as public health and communication studies, the World Health Organization Regional Office for Europe has highlighted three steps by which to address vaccine-critical activists in public spheres (see Related Summaries, below). In addition, initiatives to mobilise parents who value vaccination that have provided them with tools to engage in positive dialogue about immunisations in their communities have shown promising results. The idea here is that, if social contagion has a negative impact on vaccine acceptance (in the case of social media, for instance), such a collaborative community approach can be used to positively shift negative vaccination discourses.

In conclusion: "In the past 30 years, several vaccine controversies have traveled around the world....Vaccination resistance has always existed, but these controversies, along with outbreaks of vaccine-preventable diseases in un- or undervaccinated groups, have raised awareness among public health authorities that widespread acceptance of vaccines cannot be taken for granted....[I]t is more important than ever to pursue research to better understand community dynamics, sociocultural factors, and local knowledge, as well as how the influence of vaccine criticism may impact the acceptance of vaccines."