Overview of Tools and Measures Investigating Vaccine Hesitancy in a Ten Year Period: A Scoping Review

"The decade of vaccines (2011 to 2020) was declared by the World Health Assembly as part of the Global Vaccine Action Plan (GVAP) framework to achieve universal immunization coverage....Also, it was during this period that the use of the term 'vaccine hesitancy' was consolidated..."

The context-specific nature of vaccine hesitancy and its variability across time, place, and type of vaccine necessitates its investigation in different ways and in different settings. The result has been a plethora of studies investigating vaccine hesitancy, with some reporting on various tools and measures developed and/or adapted to investigate it. The method of development of these tools and measures varies considerably, making it difficult to compare findings across different settings, and by extension, to efficiently track variations in vaccine sentiments and to formulate standard guidelines to ensure optimum vaccination uptake. The objective of this scoping review is to provide a broad overview of tools/measures addressing vaccine hesitancy published from 2010 to 2019. Unlike an earlier similar review, it includes relevant articles of either qualitative or quantitative study design.

The researchers conducted the review using the framework for scoping reviews by Arksey and O'Malley (2005) and report it following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews' guidelines. Relevant English-language articles published in peer-reviewed journals from 2010 to 2019 were considered for inclusion in the review. Twenty-six studies were included in the final analysis.

In this review, the term "tool" is used generally to refer to author-named measures investigating vaccine hesitancy or related concepts, while the term "measure" is used to refer to unnamed measures such as questionnaires, surveys, and interview guides that are used to investigate or estimate vaccine hesitancy or related concepts. In a similar vein, an "item" in this review refers to a question assessing or exploring a specific issue of interest on a measure or tool.

Table 1 in the paper presents a snapshot of the studies and tools/measures described, with an example of each item from the tool/measure. Also presented: a major advantage or findings of the study, tool, or measure, along with a limitation of the study, or tool/measure development process as reported by the authors. A more detailed summary of the tools/measures from the literature is presented in the paper based on their primary design: 20 (77%) of the studies were of a quantitative nature, and 6 (23%) were qualitative.

Some of the quantitative tools or measures discussed include, for example: measurement of 5 psychological antecedents of vaccination, namely, confidence, constraints, complacency, calculation, and collective responsibility (referred to as the 5C scale); the Emory vaccine confidence index (EVCI); the vaccination confidence scale (VCS); the vaccine confidence index (VCI); the vaccination attitude scale (VAX scale); the parent attitudes about childhood vaccines (PACV) survey; the human papillomavirus (HPV) Attitudes and Beliefs Scale (HABS); the vaccine acceptance instrument (VAI); the vaccine conspiracy beliefs scale (VCBS); the caregiver vaccine acceptance scale (CVAS); and the vaccine attitude scale (VAS). For example, the latter (VAS) was developed and validated in Pakistan for use in low-income settings. Using 5-point Likert scale, the tool contains 2 subscales: (a) vaccine perceptions and concerns (10 items) and (b) disease salience and community benefit (4 items). The latter subscale was found to be the most concise, with the strongest association with childhood vaccination until the age of 4 months, and higher reliability than other scales identified by the authors. They recommended the 4-item subscale for routine monitoring of parental attitudes and perceptions regarding childhood vaccination, particularly in population with high burden of vaccine preventable diseases (VPDs).

Qualitative tools/measures reviewed here include, for example, one reported on in a study to understand measles vaccine hesitancy in Khartoum state, Sudan. Semi-structured interviews were conducted with 5 expanded programme on immunisation (EPI) managers and nine frontline vaccination providers. The interview guide contained a mixture of binary (yes/no) response questions, as well as open-ended and demographic questions. Most of the study participants confirmed the existence of measles vaccine hesitancy; the main contextual influence identified was the presence of people referred to as "anti-vaccination" who belong to particular religious or ethnic groups in the population.

The researchers note that most of the tools included in this review were developed by reviewing existing, relevant literature, by adapting items from existing tools, and by including some de novo items. The PACV survey seems to be the favourite tool to validate, adapt, or use as a template to develop other tools since its publication in 2011. The domain or construct most commonly investigated where indicated is "attitude". Others include concepts of trust, safety, effectiveness, and accessibility, all worded in different ways. Being developed and tested in high-income countries was the most common similarity among the tools reviewed.

A major observed difference in the reviewed tools is in the terminology used to describe the domains and/or constructs investigated. Different studies used terms such as "attitude" and "behaviour", which have different meanings, to describe or refer to constructs explored by the same or similar items. Also, the categorisation of items into scales and subscales differs for the tools reporting them, as does validation types and processes employed. The number of items ranged from a single item in one study to as many as 55 in another. A few of the tools reviewed included both a long and short form.

In reflecting on the findings, the researchers note, among other things, that:

• It would have been gratifying to see more studies reporting the use of qualitative measures included in the review. Vaccine hesitancy is a psycho-behavioural issue, and by nature, a contextual phenomenon with variability whose attributes would seem to be better explored using qualitative measures. The time frame of the review may have an influence on the retrieval of fewer studies reporting the use of qualitative measures. In the 10-year period covered, the term "vaccine hesitancy" was relatively new. This period was also before the outbreak of the COVID-19 pandemic, the advent of which brought major changes in the vaccination landscape, pushing vaccine hesitancy into the spotlight and elevating it from being just a health issue to a socio-political one. As incidence and effects of the pandemic gradually decline and the global community gradually returns to normality, it remains to be seen if there will be a change in how vaccine hesitancy is investigated and addressed.
• There is a need for validated, contextually relevant tools for vaccine hesitancy that are developed in low- and middle-income countries (LMICs). Of the 26 studies that met inclusion criteria for this review, only 3 were from LMIC settings. Of those, only one was conducted in Sub-Saharan Africa (Ghana).

The researchers discuss 3 of the tools and measures that are of particular interest to them. The first is a World Health Organization (WHO)-commissioned compendium of questions, the second is the PACV survey, and the third is the state of vaccine confidence 2016: global insights through a 67-country survey. The latter incorporates the VCI, which is a brief 4-item tool that directly explores the complex and sensitive issue of vaccines and religious compatibility as one of its items. Few of the other tools included in this review explored this issue (religion), and yet religion's "influence is strong and bears direct or indirect association in the countries where wild polio virus is still circulating..."

In conclusion, the researchers suggest that "The synopsis of the 26 included tools/measures provides useful and relevant information for researchers of different levels and interests. Those intending to validate such tools in any context or setting will find the brief, cogent insights of the review a helpful resource."