The COVID-19 pandemic highlighted the critical importance of vaccination, with South Korea achieving high overall vaccination rates. However, disparities remain at individual and regional levels. This study focuses on demand-side factors influencing these disparities, exploring how perceptions of inequality affect vaccination decisions. Extensive research has examined various determinants of vaccination uptake, including socioeconomic factors, religion, political ideology, race, ethnicity, and personal health conditions. Studies have also investigated the roles of public trust in healthcare systems, vaccine efficacy and safety perceptions, misinformation, government responses, and cultural factors. Despite this, the influence of an individual's subjective sense of inequality remains under-explored. This study aims to fill this gap by analyzing how perceptions of inequality, mediated by trust in science and society, affect vaccination behaviors in South Korea, a country with high vaccination rates but persistent regional disparities. The widening global economic disparities underscore the importance of understanding how subjective perceptions of inequality influence health decisions, particularly in democratic societies where vaccination relies on voluntary compliance.

The literature review extensively covers existing research on factors influencing vaccination adoption. Studies have shown the impact of socioeconomic and demographic factors (van Lier et al., 2014; Nagata et al., 2013; Vukovic et al., 2020), religion (Shelton et al., 2013; Eriksson and Vartanova, 2022; Wombwell et al., 2015), political ideology (Debus and Tosun, 2021; Fumgalli et al., 2023), race and ethnicity (Breaux and Rooks, 2022; Frisco et al., 2022), and personal health conditions (Daziano and Budziński, 2023; Mangtani et al., 2006; Nagata et al., 2013) on vaccine acceptance. Regarding COVID-19 vaccination, studies focused on public trust in healthcare systems (Chaudhuri et al., 2022; Fleury-Bahi et al., 2023; Moosa et al., 2022; Robinson et al., 2022), perceptions of vaccine efficacy and safety (Bullock et al., 2022; Fleury-Bahi et al., 2023; Gudayu and Mengistie, 2023; Nguyen et al., 2022; Teng et al., 2022), misinformation (Gurevich, 2022; Holman and Popușoi, 2023; Nisbet and Kamenchuk, 2021; Stier et al., 2022; Teng et al., 2022; Trujillo and Motta, 2021), social media influence (Van Nguyen and Nguyen, 2022), government responses (Boussaguet et al., 2023; Hong, 2023; Lim et al., 2022; van Espen et al., 2023), cultural dimensions (Au et al., 2023; Hong, 2023), and trust in public health institutions (Choi et al., 2023). The review also highlights the impact of political trust (Gumbi and Baba, 2024; Abayomi, 2024). However, the literature lacks a comprehensive understanding of how subjective perceptions of inequality affect vaccine-related behaviors.

This study employs a dual approach, combining individual-level survey data with district-level data from South Korea. Analysis 1 uses data from the 2021 Korean Happiness Survey (N>17,000), utilizing path analysis to examine the relationships between perceived inequality, trust in science and society, and COVID-19 vaccination attitudes. Perceived inequality is measured by a question assessing perceived income and wealth equality. Trust in science, social trust, vaccine trust, and vaccination behavior are also measured through specific survey questions. Control variables include income, education, age, political orientation, sex, homeownership, professional position, marital status, and religion. The path analysis model explores both direct and indirect effects, with trust in science and society serving as mediators. Analysis 2 shifts to the district level, using influenza vaccination data (2015-2021) across 252 administrative districts. Due to the lack of direct economic inequality data at the district level, a proxy is created using national health insurance premiums. The Palma ratio, comparing the average insurance premium of the top 10% to the bottom 40%, is used as a measure of economic inequality. Control variables at the district level include education levels, average age, male-to-female ratio, urbanization level, and hospital availability. Five different estimation techniques are employed: OLS, Fractional Probit, Random Effects (RE), and two Fixed Effects (FE) models (one with district FE and one with both district and year FE).

Analysis 1, using path analysis, found that perceived inequality significantly and negatively impacts trust in science and society. Lower trust in science and society, in turn, negatively affects vaccine trust and willingness to get vaccinated. Perceived inequality also had a direct negative effect on vaccine trust and vaccination willingness. Analysis 2, using district-level data on influenza vaccination, consistently showed a significant negative relationship between economic inequality (measured by the Palma ratio of health insurance premiums) and vaccination rates across various econometric models (OLS, Fractional Probit, RE, FE). This negative relationship persisted even after controlling for various district-level factors such as education levels, average age, gender ratio, urbanization level, and hospital availability. The results from both analyses consistently support the hypotheses that perceived inequality negatively affects trust in science and society, which in turn reduces trust in vaccines and willingness to be vaccinated. The negative relationship between inequality and vaccination rates holds across both individual-level attitudes towards COVID-19 vaccines and district-level influenza vaccination rates.

The findings demonstrate a significant and consistent negative relationship between perceived inequality and vaccination behaviors in South Korea. The study shows that perceived inequality undermines trust in science, society, and vaccines, directly and indirectly impacting vaccination uptake. This is consistent across both individual-level attitudes towards COVID-19 vaccination and aggregated district-level data on influenza vaccination. The results highlight the importance of considering not just objective economic measures but also individuals' subjective perceptions of inequality when designing public health interventions. Addressing inequality is crucial for improving vaccine uptake and fostering health equity. The study contributes to the understanding of how social and economic factors intersect with health behaviors.

This study demonstrates a clear link between perceived inequality, trust in institutions, and vaccination rates in South Korea. The dual-level analysis reveals the importance of considering subjective experiences of inequality when designing public health policies. Future research should explore this relationship in diverse cultural contexts and utilize longitudinal data to establish causality. Addressing economic inequality is crucial for enhancing public health and promoting social cohesion.

The study relies on single-item measures for some key constructs, limiting the reliability and validity of the findings. The cross-sectional nature of the individual-level data limits causal inferences, and potential unobserved confounders might influence the results. The use of health insurance premiums as a proxy for district-level inequality might introduce measurement error. Future studies should address these limitations through the use of multiple-item measures, longitudinal designs, and more direct measures of economic inequality.