The COVID-19 pandemic presented unprecedented challenges globally, with fragile and conflict-affected settings (FCS) disproportionately impacted due to pre-existing strained resources and humanitarian crises. High-income nations could readily redirect resources to understand vaccination coverage determinants, while FCS nations relied on global bodies for vaccines and essential medications. This disparity highlighted the urgent need to identify factors influencing vaccine uptake in FCS contexts. The study uses the Council on Social Determinants of Health (CSDH) framework, which posits that social, economic, political, and health system factors significantly influence health outcomes. The researchers hypothesized that these factors would play a crucial role in explaining disparities in COVID-19 vaccination coverage between FCS and non-FCS countries. Understanding these determinants is critical for developing context-specific vaccination strategies and achieving equitable vaccine access globally. The study's importance lies in its potential to inform resource allocation, policy formulation, and the creation of enabling environments to enhance vaccine equity in vulnerable settings, ultimately improving population health outcomes in the face of future pandemics.

Existing literature extensively documents the impact of the COVID-19 pandemic and the challenges faced by FCS countries. Studies on past outbreaks, such as Ebola, demonstrate that indirect health effects can significantly exceed direct mortality and morbidity. The UN Security Council resolution 2565 (2021) acknowledged the exacerbating effect of armed conflicts on the pandemic and vice versa. Research on healthcare access in non-FCS settings often focuses on individual-level factors like availability, affordability, and attitudes. However, in FCS, factors such as disrupted supply chains, conflict, and weak infrastructure significantly impact vaccine availability and accessibility. Studies have shown inequitable vaccine distribution globally, with high-income countries procuring far more doses than low-income countries. The COVAX facility, while aiming for equitable distribution, faces substantial challenges in reaching its targets. Previous research emphasizes the need to understand COVID-19 vaccination coverage determinants from a contextual perspective, considering social, economic, health system, governance, and political factors. The study builds upon this literature by explicitly comparing FCS and non-FCS countries and applying the CSDH framework to analyze vaccine inequities.

This study employed a quantitative, cross-country comparative design. Data on COVID-19 cases, deaths, vaccinations, and various determinants were compiled from publicly available databases, including Our World in Data (OWID), WHO, Global Health Security Index, United Nations, and World Bank. The World Bank's classification of FCS states served as the primary source for country classification, identifying 39 FCS countries. The outcome variable was the share of the population with at least one COVID-19 vaccine dose by July 2021. The study incorporated various independent variables, categorized as socioeconomic (GDP per capita, socioeconomic resilience index), health system (Global Health Security Index score, human resources for health, health expenditure), and political (government effectiveness, political stability, individual liberty). Vaccine preference was proxied using data on general vaccine confidence from De Figueiredo et al. Multi-variate log-linear regressions were conducted separately for FCS and non-FCS country samples to assess the relationship between COVID-19 vaccine coverage and the independent variables. The study conducted sensitivity analyses to ensure robustness to different definitions of vaccine coverage and performed diagnostic tests to address potential endogeneity issues (omitted variable bias, linearity, multi-collinearity, and heteroskedasticity).

The study revealed significant differences in COVID-19 caseloads, deaths, and vaccination coverage between FCS and non-FCS countries. FCS countries had lower cumulative cases and deaths but higher case fatality rates. Socioeconomic factors explained a substantial portion of the variation in vaccine coverage in both groups (66% in non-FCS and 48% in FCS). GDP per capita and socioeconomic resilience were strongly associated with higher vaccination rates. Demographic factors, while showing some effects, were not statistically significant once socioeconomic factors were controlled for. Health system factors explained less variation than socioeconomic factors, but human resources for health and domestic health spending emerged as significant predictors. Political factors, particularly government effectiveness and political stability, played a stronger role in FCS countries. Interestingly, while equality before the law and individual liberty showed a positive correlation initially, after controlling for other factors, this relationship was negative and statistically significant for FCS countries. The combined model, including socioeconomic, health system, and political factors, explained 68% and 62% of the variation in vaccine coverage for non-FCS and FCS countries respectively. Vaccine preference, proxied by confidence in vaccine effectiveness, showed a positive association with vaccination coverage in FCS countries, contrary to its effect in non-FCS countries.

The findings confirm that COVID-19 vaccine coverage is influenced by a complex interplay of socioeconomic, health system, and political factors, varying in relative importance between FCS and non-FCS settings. The strong influence of socioeconomic factors highlights the crucial role of poverty reduction and socioeconomic development in enhancing vaccine access and uptake. The significant effect of government effectiveness underscores the importance of strong governance structures for effective vaccine rollout and campaign implementation. The contrasting effects of vaccine preference between the two groups highlight the need for context-specific strategies addressing vaccine hesitancy. The negative effect of indicators of equality and liberty requires further investigation into potential mediating factors. These findings strongly support the CSDH framework and emphasize the importance of adopting holistic, multisectoral approaches to address vaccine inequities.

This study provides crucial evidence on the social determinants of COVID-19 vaccination coverage in FCS and non-FCS countries. The findings highlight the importance of addressing socioeconomic inequalities, strengthening governance and health systems, and tailoring strategies to address context-specific challenges, particularly vaccine hesitancy. Further research should explore the complex relationship between perceived equality, individual liberty, and vaccine uptake, particularly in FCS settings. Addressing global vaccine inequities requires inclusive policies and international cooperation to ensure equitable access to vaccines and essential resources for all, especially in vulnerable populations.

The study's limitations include the use of country-level averages, potentially masking within-country variations. Data merging from multiple sources may introduce inconsistencies. The smaller sample size of FCS countries limits the generalizability of findings related to this group, requiring caution in interpreting the results. The study's results are sensitive to the date of data collection and the availability of more comprehensive datasets could enhance analysis and refine conclusions.