Despite being recognized as one of the most successful public health measures, vaccination is perceived as unsafe and unnecessary by a growing number of individuals. Lack of confidence in vaccines is now considered a threat to the success of vaccination programs. Vaccine hesitancy is believed to be responsible for decreasing vaccine coverage and an increasing risk of vaccine-preventable disease outbreaks and epidemics. This review provides an overview of the phenomenon of vaccine hesitancy. First, we will characterize vaccine hesitancy and suggest the possible causes of the apparent increase in vaccine hesitancy in the developed world. Then we will look at determinants of individual decision-making about vaccination.

In March 2012, the SAGE Working Group on Vaccine Hesitancy was convened to define the term "vaccine hesitancy", as well as to map the determinants of vaccine hesitancy and develop tools to measure and address the nature and scale of hesitancy in settings where it is becoming more evident. The definition of vaccine hesitancy and a matrix of determinants guided the development of a survey tool to assess the nature and scale of hesitancy issues. Additionally, vaccine hesitancy questions were piloted in the annual WHO-UNICEF joint reporting form, completed by National Immunization Managers globally. The objective of characterizing the nature and scale of vaccine hesitancy issues is to better inform the development of appropriate strategies and policies to address the concerns expressed, and to sustain confidence in vaccination. The Working Group developed a matrix of the determinants of vaccine hesitancy informed by a systematic review of peer reviewed and grey literature, and by the expertise of the working group. The matrix mapped the key factors influencing the decision to accept, delay or reject some or all vaccines under three categories: contextual, individual and group, and vaccine-specific. These categories framed the menu of survey questions presented in this paper to help diagnose and address vaccine hesitancy.

Despite being recognized as one of the most successful public health measures, vaccination is perceived as unsafe and unnecessary by a growing number of parents. Anti-vaccination movements have been implicated in lowered vaccine acceptance rates and in the increase in vaccine-preventable disease outbreaks and epidemics. In this review, we will look at determinants of parental decision-making about vaccination and provide an overview of the history of anti-vaccination movements and its clinical impact.

When faced with vaccine hesitancy, public health authorities are looking for effective strategies to address this issue. In this paper, the findings of 15 published literature reviews or meta-analysis that have examined the effectiveness of different interventions to reduce vaccine hesitancy and/or to enhance vaccine acceptance are presented and discussed. From the literature, there is no strong evidence to recommend any specific intervention to address vaccine hesitancy/refusal. The reviewed studies included interventions with diverse content and approaches that were implemented in different settings and targeted various populations. Few interventions were directly targeted to vaccine hesitant individuals. Given the paucity of information on effective strategies to address vaccine hesitancy, when interventions are implemented, planning a rigorous evaluation of their impact on vaccine hesitancy/vaccine acceptance will be essential.

The term vaccine hesitancy refers to delay in acceptance or refusal of vaccines despite the availability of vaccination services. Different factors influence vaccine hesitancy and these are context-specific, varying across time and place and with different vaccines. Factors such as complacency, convenience and confidence are involved. Acceptance of vaccines may be decreasing and several explanations for this trend have been proposed. The WHO Strategic Advisory Group of Experts (SAGE) on Immunization has recognized the global importance of vaccine hesitancy and recommended an interview study with immunization managers (IMs) to better understand the range of vaccine hesitancy determinants that are encountered in different settings. Interviews with IMs in 13 selected countries were conducted between September and December 2013 and various factors that discourage vaccine acceptance were identified. Vaccine hesitancy was not defined consistently by the IMs and most interpreted the term as meaning vaccine refusal. Although vaccine hesitancy existed in all 13 countries, some IMs considered its impact on immunization programmes to be a minor problem. The causes of vaccine hesitancy varied in the different countries and were context-specific, indicating a need to strengthen the capacity of national programmes to identify the locally relevant causal factors and to develop adapted strategies to address them.

An often-stated public health comment is that “vaccination is a victim of its own success.” While the scientific and medical consensus on the benefits of vaccination is clear and unambiguous, an increasing number of people are perceiving vaccines as unsafe and unnecessary. The World Health Organization identified “the reluctance or refusal to vaccinate despite availability of vaccines” as one of the 10 threats to global health in 2019. The negative influence of anti-vaccination movements is often named as a cause of increasing vaccine resistance in the public. In this review, we give an overview of the current literature on the topic, beginning by agreeing on terminology and concepts before looking at potential causes, consequences, and impacts of resistance to vaccination.