Vaccine Hesitancy: Definition, Scope and Determinants

"Vaccine hesitancy is complex and context specific, varying across time, place and vaccines. It is influenced by factors such as complacency, convenience and confidence."

As detailed here, the Vaccine Hesitancy Determinants Matrix displays the factors influencing the behavioural decision to accept, delay, or reject some or all vaccines under 3 categories: contextual, individual and group, and vaccine/vaccination-specific influences. It was developed by the SAGE Working Group on Vaccine Hesitancy (hereafter, WG), which defines vaccine hesitancy as delay in acceptance or refusal of vaccination despite availability of vaccination services. Hesitancy is set on a continuum between those that accept all vaccines with no doubts, to complete refusal with no doubts, with vaccine hesitant individuals the heterogeneous group between these two extremes (see Figure 1). "Vaccine hesitancy may be present in situations where vaccination uptake is low because of system failures, e.g. stock-outs, limited availability of vaccination services (time, place, etc.), curtailment of vaccine services in the presence of conflict or natural disaster, but in these situations hesitancy is not the main explanation for the presence of unvaccinated or under-vaccinated members of the population."

The report then clarifies the difference between vaccine hesitancy and vaccine demand: "An individual or community may fully accept vaccination without hesitancy but may not demand vaccination or a specific vaccine." Examples are provided to illustrate the distinction.

In 2012, the WG reviewed a number of conceptual models for grouping vaccine hesitancy determinants. The "3 Cs" model, first proposed to the World Health Organization (WHO) Regional Office for Europe (EURO) Vaccine Communications Working Group in 2011, highlights:

1. Confidence, which is defined as trust in: (i) the effectiveness and safety of vaccines; (ii) the system that delivers them, including the reliability and competence of the health services and health professionals; and (iii) the motivations of policymakers who decide on the needed vaccines.
2. Complacency, which exists where perceived risks of vaccine-preventable diseases are low and vaccination is not deemed a necessary preventive action. "Immunization programme success may, paradoxically, result in complacency and ultimately, hesitancy, as individuals weigh risks of vaccination with a particular vaccine against risks of the disease the vaccine prevents that disease is no longer common. Self-efficacy (the self-perceived or real ability of an individual to take action to be vaccinated) also influences the degree to which complacency determines hesitancy."
3. Convenience, which involves factors that affect uptake, such as ability to understand (language and health literacy) and appeal of immunisation services. "The quality of the service (real and/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 affect the decision to be vaccinated and could lead to vaccine hesitancy."

Table one shows the WG's Vaccine Hesitancy Determinants Matrix, which - while not primarily intended as a practical tool - may be helpful for researchers, survey question developers, and those developing interventions to address hesitancy. In brief, it includes:

• Contextual influences arising due to historic, socio-cultural, environmental, health system/institutional, economic, or political factors. Example: the communication and media environment.
• Individual and group influences arising from personal perception of the vaccine or influences of the social/peer environment. Example: personal, family, and/or community members' experience with vaccination, including pain.
• Vaccine/vaccination (specific issues directly related to vaccine or vaccination). Example: the strength of the recommendation and/or knowledge base and/or attitude of healthcare professionals.

The WG concluded that communication is a tool, not a determinant. "[W]hen it is poor or inadequate, it can negatively influence vaccination uptake and contribute to vaccine hesitancy....In low and middle income countries, scarce communication resources limit the capacity to counter negative information about vaccines and achieve community support for vaccination programs. For instance, the Independent Monitoring Board on Polio Eradication noted deep concern about "the Global Programme's weak grip on the communications and social mobilization that could not just neutralize communities' negativity, but generate more genuine demand. Within the Programme, communications is the poor cousin of vaccine delivery, undeservedly receiving far less focus. Communications expertise is sparse throughout and needs to be strengthened".