Low-income countries had 21% lower overall health service coverage scores than high-income countries.
Infectious disease services showed the widest income gap, at 31%.
A study of 194 countries found that higher human development was linked to better healthcare coverage.
Researchers said development beyond the health sector was important for improving access to healthcare.
Countries with higher levels of human development generally had better universal health coverage (UHC), with disparities between income groups often greater than differences between world regions, according to a new study published in the journal PLOS Global Public Health.
Universal health coverage means that everyone can access the quality health services they need, when and where they need them, without facing financial hardship. Achieving UHC is a key target of the United Nations-mandated Sustainable Development Goals.
UHC and human development are closely linked, as greater access to preventive care, health screenings and vaccinations can contribute to better health outcomes.
Health service coverage is measured using the UHC Service Coverage Index (SCI), which covers four areas: reproductive, maternal, newborn and child health; infectious diseases; non-communicable diseases; and service capacity and access.
Researchers led by Akira Hayasaka of Yokohama City University, Japan, analysed the relationship between health service coverage and the Human Development Index (HDI), using World Health Organization (WHO) and UN data from 194 countries.
The study found persistent disparities between income groups in overall health service coverage, infectious disease services, service capacity and access, and human development.
The gaps were smaller for reproductive, maternal, newborn and child health services, and less pronounced for non-communicable diseases.
Low-income countries had overall UHC service coverage scores 21 per cent lower than high-income countries. The largest disparity was in infectious disease services, where coverage scores were 31 per cent lower.
These income-related disparities were generally greater than differences between world regions.
The researchers also found that a 0.1-point increase in HDI was associated with a 6.8-point increase in the overall UHC service coverage score.
The strongest association was observed in service capacity and access, where the corresponding increase was 11.7 points. The weakest was for non-communicable diseases, at 2.2 points.
However, regional inequalities remained significant. The study found that the WHO African Region had markedly lower adjusted service capacity and access scores than the European Region.
According to the researchers, these findings indicate that progress towards universal health coverage remains closely linked to broader development conditions and differences in health system capacity.
The study examined national-level data rather than individual experiences, meaning it could not capture inequalities in healthcare access within countries.
The researchers also cautioned that changes to the indicators used in the UHC index over time limited comparisons between different editions of the report.
Nevertheless, they concluded that higher levels of human development were associated with better health service coverage, although the strength of the relationship varied across healthcare services.
“These findings may help policymakers interpret the UHC SCI and its sub-indices in the context of their country's broader development trajectory,” the researchers said.
“Higher levels of human development were associated with better health service coverage, although the strength of this relationship differed across domains,” they added.
The researchers said the findings showed that development in sectors beyond healthcare was also associated with access to health services, offering insights for policies aimed at improving health coverage worldwide.
