Validation of the Vaccination Trust Indicator (VTI) in a Multi-country Survey of Adult Vaccination Attitudes

"The VTI is a promising tool for assessing adult immunization attitudes with clear and immediate uses for immunization programs globally."

Vaccine hesitancy is a driver of low vaccine uptake among adults, but it is argued that scales that measure vaccine attitudes do not adequately capture general vaccination attitudes in this population. This study uses data from two surveys of adult vaccine attitudes and uptake conducted in 15 countries to evaluate the Vaccination Trust Indicator (VTI). The 6-item is envisioned as a psychometrically viable yet easily administered tool that is relevant to a broad context of global settings, including low- and middle-income countries (LMICs).

The items included in the VTI represent core constructs previously demonstrated to be associated with vaccine confidence, including trust in key vaccine stakeholders, vaccine knowledge and vaccine effectiveness, and self-efficacy. Each item in the VTI utilises an 11-point Likert scale (0-10), with lower scores representing disagreement with the statement and higher scores representing agreement. The score is an unweighted average of the participants' responses to each question and scaled to a 100-point scale.

The overall study sample contained 9,809 participants, with responses varying from 400-850 within each country. Fifteen countries were included, although self-reported influenza and tetanus vaccine receipt information was only available for 5 of them. The overall average VTI score was 73.8 (standard deviation (SD) = 18.5). The Philippines had the highest average score (83.8, SD = 14.4), and France and China had the lowest VTI scores (64.3, SD = 19.8 and 14.9, respectively). Most participants were categorised as having high trust in vaccines (61%) or moderate trust in vaccines (33%). Only 5% of participants were categorised as having low trust in vaccines.

The researchers used multivariable logistic regression to examine the association between VTI scores and self-reported receipt of the seasonal influenza vaccine, receipt of a tetanus toxoid-containing vaccine, and intent to receive the flu vaccine in the next season. In the 5 countries with self-reported vaccine receipt data (China, France, Mexico, United Kingdom (UK), and United States - US), the researchers found that a 10-point increase in VTI score was associated with a 50% increase in odds of influenza vaccine receipt (odds ratio (OR) = 1.55, 95% confidence interval (CI) = 1.48, 1.62) and 25% increase in the odds of tetanus vaccine receipt (OR = 1.26, 95% CI = 1.21, 1.30). Strong associations between VTI score and vaccine receipt were found in each country except China. A strong association between VTI score and intent to receive the influenza vaccine was found in all 15 countries.

To look at the findings about one vaccine in particular, a 10-point increase in VTI score was associated with increasing odds of intent to receive the influenza vaccine in the next flu season, although the strength of the association varied by country. When individuals were placed in vaccine acceptance categories (VTI ≤ 40, low vaccine acceptance; 41–70, moderate vaccine acceptance; ≥ 71, high vaccine acceptance), those with moderate trust in vaccination were over 4 times more likely to have the intention to receive the influenza vaccine than those with low trust in vaccines (OR = 4.63, 95% CI = 3.44, 6.38). Individuals with high trust in vaccines were nearly 20 times more likely to intend to get the flu vaccine (OR = 19.81, 95% CI = 14.78, 27.19).

In reflecting on the VTI's strengths, the researchers note that it can be utilised to measure attitudes about any adult vaccines. The analyses have demonstrated that the VTI is valid measure of vaccine attitudes in non-Western, non-high-income countries. Furthermore, nearly all of the existing scales include 10 or more items, limiting use as a rapid diagnostic tool; in contrast, the 6-item VTI can be used to rapidly categorise individuals into "high", "moderate", or "low" levels of trust in vaccines, making it potentially useful in the intervention setting.

In conclusion: "To understand and address vaccine hesitancy, vaccination programs need to be able to measure and track vaccine confidence. This is important in efforts to increase uptake of existing vaccines, like the seasonal influenza and tetanus vaccines, but has been shown to be vitally important for COVID-19 vaccination programs."