A study in PLOS Global Public Health in April 2023 presents a validation of the Vaccination Trust Indicator (VTI) with data from two surveys across 15 countries. It is described as a “promising tool” to help researchers understand adult immunisation attitudes with “clear and immediate uses for immunisation programmes globally”.
The VTI is a 6-item measure that is “intended to capture general vaccine attitudes”. The study authors describe the goal as “to create a psychometrically viable yet easily administered tool that is relevant to a broad context of global settings”. The “potential applications” of this tool include:
- Rapid evaluation of general levels of vaccine confidence in individuals or populations at a given point in time
- Monitoring levels of general vaccine confidence in a population over time
- Evaluating the effectiveness of interventions designed to improve in vaccine confidence among adults
The six items in the scale represent a “small subset” of a large 120-item vaccination attitudes survey. These six were selected based on “preliminary analyses” from a 2013/2014 survey by Double Helix. These identified the “unique items most highly correlated with” with the statement “I generally trust vaccination”. To see the table of these items, access the study here.
Each item uses an 11-point Likert scale (0-10). Lower scores are associated with disagreement with the statement and higher scores represent agreement. The authors describe the score as an “unweighted average” of the responses to each question and scaled to a 100-point scale.
The importance of vaccination
“Vaccines are one of the greatest tools available to combat infectious disease.”
The authors highlight the significance of childhood immunisation programmes, a “monumental health success”. These programmes continue to prevent millions of deaths due to vaccine preventable diseases. However, “communicable disease continues to contribute substantially to global morbidity and mortality” despite the availability of vaccines against common infectious diseases among adults.
“This burden is not shared equally, with the majority of infections and deaths due to vaccine preventable diseases among the elderly, individuals with underlying health conditions, displaced populations, and those living in low- and middle-income countries.”
These “patterns” were emphasised during the COVID-19 pandemic. The study indicates that, in light of the continuing pandemic, improved vaccine uptake among adults could “substantially decrease this burden of disease”. Many countries fail to achieve high vaccination rates with vaccines such as influenza, and tetanus vaccine recommendations “vary”.
“The varied implementation of adult vaccine programmes and the patchy availability of adult vaccinations globally contribute to low coverage but cannot entirely explain vaccine uptake among adults.”
Using the WHO definition of vaccine hesitancy, the authors imply that the “motivational state” of vaccine attitudes better explain past vaccine behaviour than demographic or socioeconomic factors. Despite acknowledgement that hesitancy is “emerging as a potential barrier” to vaccination campaigns, the authors suggest that previous studies have not used “consistent measures of vaccine hesitancy that have been validated against meaningful outcomes such as intention to vaccinate or actual vaccination behaviour”.
The study aims to validate the VTI among adults in self-reported influenza and tetanus vaccine receipt in 5 countries: US, UK, Mexico, France, and China. It also considers intention to receive the influenza vaccine in the same 5 countries alongside 10 more: Australia, India, Indonesia, Malaysia, Thailand, Vietnam, the Philippines, Taiwan, Singapore, and Poland.
The analysis is a “secondary analysis of existing data” from two studies that incorporated the VTI in surveys. The first study was conducted at the end of the 2013/2014 influenza season in the US, Uk, and France, and at the end of the 2014/2015 influenza season in China and Mexico. The second study expanded to the ten additional countries at the end of each region’s 2015/2016 influenza season.
“Survey items were adjusted to be culturally relevant in each country.”
Participants were at least 18 years old and had obtained a high school education. They lived in urban settings. A combination of online self-completion surveys and “random digit dialing” was used to reach a “necessary proportion of 65+ and socioeconomic groups that may not have as much access to or familiarity with internet resources”.
“Trust is a foundational component of vaccine acceptance; trust not just in the vaccines, but also in the provider of the vaccines – healthcare workers, public health authorities and governments.”
Previous studies that the authors refer to have shown that trust in various organisations and individuals is “correlated with uptake” of specific vaccines. Indeed, contemporary examples from the COVID-19 pandemic demonstrate that trust in authorities and “vaccine stakeholders” is emerging as a “key determinant of public acceptance” of the vaccines.
“We may therefore expect that post-COVID-19 the VTI may be an even stronger indicator of vaccine intentions and uptake.”
What does the study show?
The authors state that the results of their study indicate that the WTI has the “potential to be a valid and accurate measure of adult vaccine attitudes in both individuals and populations”. Across the 5 countries with self-reported vaccine receipt data, they found that a ten-point increase in VTI score was associated with a 50% increase in odds of self-reported influenza vaccine receipt.
Although the strength of association between VTI scores and self-reported receipt varied by country, the authors believe this is a “reflection of differing adult immunisation policies by country”. For example, there was a “null or weak association between VTI score and both influenza and Tdap vaccine receipt in China”. However, at the time of the survey the general adult population had not been recommended uptake.
The overall conclusion of the paper is that VTI is a “valid measure” of vaccine attitudes in “non-Western, non-high-income countries”. It will also be “very useful in the intervention setting”.
“The VTI is a promising tool for assessing adult immunisation attitudes with clear and immediate uses for immunisation programmes globally.”
The researchers recommend that countries “consider monitoring trust in vaccination among adults with the VTI” to “inform country readiness” and “demand generation activities” for vaccination programmes.
Do you agree that the VTI is a “valid measure” of vaccine attitudes? To access the study in full please follow this link.